# PaCkAgE DaTaStReAm
autoconf 1 6572
# end of header
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CLASSES=none
CATEGORY=utility
ARCH=sparc
DESC=GNU autoconf m4 macro creator
EMAIL=http://www.gnu.org/software/autoconf/
VENDOR=GNU
PSTAMP=4th March 2014
VERSION=2.69
NAME=GNU autoconf 2.69 SPARC 64bit Solaris 11
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1 f none /usr/local/share/man/man1/autom4te.1 0644 root root 4635 64 1393911188
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DESC=GNU autoconf m4 macro creator
EMAIL=http://www.gnu.org/software/autoconf/
VENDOR=GNU
PSTAMP=4th March 2014
VERSION=2.69
NAME=GNU autoconf 2.69 SPARC 64bit Solaris 11
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0707010000cb8e000041ed0000000000000000000000025315661a000000000000011f00010018ffffffffffffffff0000000800000000install 0707010000cb8f000081ed00000000000000000000000153156617000003110000011f00010018ffffffffffffffff0000001500000000install/checkinstall #!/bin/sh
#
expected_bits="64"
expected_release="5.11"
expected_platform="sparc"
#
release=`uname -r`
platform=`uname -p`
bits=`isainfo -b`
#
if [ ${platform} != ${expected_platform} ]; then
echo "\n\n\n\tThis package must be installed on a ${expected_platform} architecture\n"
echo "\tAborting installation.\n\n\n"
exit 1
fi
if [ ${release} != ${expected_release} ]; then
echo "\n\n\n\tThis package must be installed on a ${expected_release} machine\n"
echo "\tAborting installation.\n\n\n"
exit 1
fi
if [ ${bits} != ${expected_bits} ]; then
echo "\n\n\n\tThis package must be installed on a ${expected_bits} bit machine\n"
echo "\tYour machine is running a ${bits} bit O.S. currently\n"
echo "\tAborting installation.\n\n\n"
exit 1
fi
exit 0
0707010000cb40000041ed0000000000000000000000035315661a000000000000011f00010018ffffffffffffffff0000000500000000root 0707010000cb41000041ed0000000000000000000000035315661a000000000000011f00010018ffffffffffffffff0000000900000000root/usr 0707010000cb42000041ed0000000000000000000000045315661a000000000000011f00010018ffffffffffffffff0000000f00000000root/usr/local 0707010000cb4c000041ed0000000000000000000000055315661a000000000000011f00010018ffffffffffffffff0000001500000000root/usr/local/share 0707010000cb83000041ed0000000000000000000000035315661a000000000000011f00010018ffffffffffffffff0000001900000000root/usr/local/share/man 0707010000cb84000041ed0000000000000000000000025315661a000000000000011f00010018ffffffffffffffff0000001e00000000root/usr/local/share/man/man1 0707010000cb87000081a4000000000000000000000001531565940000121b0000011f00010018ffffffffffffffff0000002900000000root/usr/local/share/man/man1/autom4te.1 .\" DO NOT MODIFY THIS FILE! It was generated by help2man 1.40.8.
.TH AUTOM4TE "1" "April 2012" "GNU Autoconf 2.68b.25-19513" "User Commands"
.SH NAME
autom4te \- Generate files and scripts thanks to M4
.SH SYNOPSIS
.B autom4te
[\fIOPTION\fR]... [\fIFILES\fR]
.SH DESCRIPTION
Run GNU M4 on the FILES, avoiding useless runs. Output the traces if tracing,
the frozen file if freezing, otherwise the expansion of the FILES.
.PP
If some of the FILES are named `FILE.m4f' they are considered to be M4
frozen files of all the previous files (which are therefore not loaded).
If `FILE.m4f' is not found, then `FILE.m4' will be used, together with
all the previous files.
.PP
Some files may be optional, i.e., will only be processed if found in the
include path, but then must end in `.m4?'; the question mark is not part of
the actual file name.
.SS "Operation modes:"
.TP
\fB\-h\fR, \fB\-\-help\fR
print this help, then exit
.TP
\fB\-V\fR, \fB\-\-version\fR
print version number, then exit
.TP
\fB\-v\fR, \fB\-\-verbose\fR
verbosely report processing
.TP
\fB\-d\fR, \fB\-\-debug\fR
don't remove temporary files
.TP
\fB\-o\fR, \fB\-\-output\fR=\fIFILE\fR
save output in FILE (defaults to `\-', stdout)
.TP
\fB\-f\fR, \fB\-\-force\fR
don't rely on cached values
.TP
\fB\-W\fR, \fB\-\-warnings\fR=\fICATEGORY\fR
report the warnings falling in CATEGORY
.TP
\fB\-l\fR, \fB\-\-language\fR=\fILANG\fR
specify the set of M4 macros to use
.TP
\fB\-C\fR, \fB\-\-cache\fR=\fIDIRECTORY\fR
preserve results for future runs in DIRECTORY
.TP
\fB\-\-no\-cache\fR
disable the cache
.TP
\fB\-m\fR, \fB\-\-mode\fR=\fIOCTAL\fR
change the non trace output file mode (0666)
.TP
\fB\-M\fR, \fB\-\-melt\fR
don't use M4 frozen files
.SS "Languages include:"
.TP
`Autoconf'
create Autoconf configure scripts
.TP
`Autotest'
create Autotest test suites
.TP
`M4sh'
create M4sh shell scripts
.TP
`M4sugar'
create M4sugar output
.SS "Warning categories include:"
.TP
`cross'
cross compilation issues
.TP
`gnu'
GNU coding standards (default in gnu and gnits modes)
.TP
`obsolete'
obsolete features or constructions
.TP
`override'
user redefinitions of Automake rules or variables
.TP
`portability'
portability issues (default in gnu and gnits modes)
.TP
`syntax'
dubious syntactic constructs (default)
.TP
`unsupported'
unsupported or incomplete features (default)
.TP
`all'
all the warnings
.TP
`no\-CATEGORY'
turn off warnings in CATEGORY
.TP
`none'
turn off all the warnings
.TP
`error'
treat warnings as errors
.PP
The environment variables `M4' and `WARNINGS' are honored.
.SS "Library directories:"
.TP
\fB\-B\fR, \fB\-\-prepend\-include\fR=\fIDIR\fR
prepend directory DIR to search path
.TP
\fB\-I\fR, \fB\-\-include\fR=\fIDIR\fR
append directory DIR to search path
.SS "Tracing:"
.TP
\fB\-t\fR, \fB\-\-trace\fR=\fIMACRO[\fR:FORMAT]
report the MACRO invocations
.TP
\fB\-p\fR, \fB\-\-preselect\fR=\fIMACRO\fR
prepare to trace MACRO in a future run
.SS "Freezing:"
.TP
\fB\-F\fR, \fB\-\-freeze\fR
produce an M4 frozen state file for FILES
.SS "FORMAT defaults to `$f:$l:$n:$%', and can use the following escapes:"
.TP
$$
literal $
.TP
$f
file where macro was called
.TP
$l
line where macro was called
.TP
$d
nesting depth of macro call
.TP
$n
name of the macro
.TP
$NUM
argument NUM, unquoted and with newlines
.TP
$SEP@
all arguments, with newlines, quoted, and separated by SEP
.TP
$SEP*
all arguments, with newlines, unquoted, and separated by SEP
.TP
$SEP%
all arguments, without newlines, unquoted, and separated by SEP
.PP
SEP can be empty for the default (comma for @ and *, colon for %),
a single character for that character, or {STRING} to use a string.
.SH AUTHOR
Written by Akim Demaille.
.SH "REPORTING BUGS"
Report bugs to .
.br
GNU Autoconf home page: .
.br
General help using GNU software: .
.SH COPYRIGHT
Copyright \(co 2012 Free Software Foundation, Inc.
License GPLv3+/Autoconf: GNU GPL version 3 or later
,
.br
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
.SH "SEE ALSO"
.BR autoconf (1),
.BR automake (1),
.BR autoreconf (1),
.BR autoupdate (1),
.BR autoheader (1),
.BR autoscan (1),
.BR config.guess (1),
.BR config.sub (1),
.BR ifnames (1),
.BR libtool (1).
.PP
The full documentation for
.B autom4te
is maintained as a Texinfo manual. If the
.B info
and
.B autom4te
programs are properly installed at your site, the command
.IP
.B info autom4te
.PP
should give you access to the complete manual.
0707010000cb8a000081a400000000000000000000000153156594000007e50000011f00010018ffffffffffffffff0000002b00000000root/usr/local/share/man/man1/autoupdate.1 .\" DO NOT MODIFY THIS FILE! It was generated by help2man 1.40.8.
.TH AUTOUPDATE "1" "April 2012" "GNU Autoconf 2.68b.25-19513" "User Commands"
.SH NAME
autoupdate \- Update a configure.in to a newer Autoconf
.SH SYNOPSIS
.B autoupdate
[\fIOPTION\fR]... [\fITEMPLATE-FILE\fR]...
.SH DESCRIPTION
Update each TEMPLATE\-FILE if given, or `configure.ac' if present,
or else `configure.in', to the syntax of the current version of
Autoconf. The original files are backed up.
.SS "Operation modes:"
.TP
\fB\-h\fR, \fB\-\-help\fR
print this help, then exit
.TP
\fB\-V\fR, \fB\-\-version\fR
print version number, then exit
.TP
\fB\-v\fR, \fB\-\-verbose\fR
verbosely report processing
.TP
\fB\-d\fR, \fB\-\-debug\fR
don't remove temporary files
.TP
\fB\-f\fR, \fB\-\-force\fR
consider all files obsolete
.SS "Library directories:"
.TP
\fB\-B\fR, \fB\-\-prepend\-include\fR=\fIDIR\fR
prepend directory DIR to search path
.TP
\fB\-I\fR, \fB\-\-include\fR=\fIDIR\fR
append directory DIR to search path
.SH AUTHOR
Written by David J. MacKenzie and Akim Demaille.
.SH "REPORTING BUGS"
Report bugs to .
.br
GNU Autoconf home page: .
.br
General help using GNU software: .
.SH COPYRIGHT
Copyright \(co 2012 Free Software Foundation, Inc.
License GPLv3+/Autoconf: GNU GPL version 3 or later
,
.br
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
.SH "SEE ALSO"
.BR autoconf (1),
.BR automake (1),
.BR autoreconf (1),
.BR autoupdate (1),
.BR autoheader (1),
.BR autoscan (1),
.BR config.guess (1),
.BR config.sub (1),
.BR ifnames (1),
.BR libtool (1).
.PP
The full documentation for
.B autoupdate
is maintained as a Texinfo manual. If the
.B info
and
.B autoupdate
programs are properly installed at your site, the command
.IP
.B info autoupdate
.PP
should give you access to the complete manual.
0707010000cb8c000081a400000000000000000000000153156594000004ce0000011f00010018ffffffffffffffff0000002b00000000root/usr/local/share/man/man1/config.sub.1 .\" DO NOT MODIFY THIS FILE! It was generated by help2man 1.40.8.
.TH CONFIG.SUB "1" "April 2012" "GNU Autoconf 2.68b.25-19513" "User Commands"
.SH NAME
config.sub \- validate and canonicalize a configuration triplet
.SH SYNOPSIS
.B config.sub
[\fIOPTION\fR] \fICPU-MFR-OPSYS\fR
.SH DESCRIPTION
.IP
\&../build\-aux/config.sub [OPTION] ALIAS
.PP
Canonicalize a configuration name.
.SS "Operation modes:"
.TP
\fB\-h\fR, \fB\-\-help\fR
print this help, then exit
.TP
\fB\-t\fR, \fB\-\-time\-stamp\fR
print date of last modification, then exit
.TP
\fB\-v\fR, \fB\-\-version\fR
print version number, then exit
.SH "REPORTING BUGS"
Report bugs and patches to .
.SH COPYRIGHT
Copyright \(co 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012
Free Software Foundation, Inc.
.PP
.br
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
.SH "SEE ALSO"
.BR autoconf (1),
.BR automake (1),
.BR autoreconf (1),
.BR autoupdate (1),
.BR autoheader (1),
.BR autoscan (1),
.BR config.guess (1),
.BR config.sub (1),
.BR ifnames (1),
.BR libtool (1).
0707010000cb86000081a40000000000000000000000015315659400000a580000011f00010018ffffffffffffffff0000002b00000000root/usr/local/share/man/man1/autoheader.1 .\" DO NOT MODIFY THIS FILE! It was generated by help2man 1.40.8.
.TH AUTOHEADER "1" "April 2012" "GNU Autoconf 2.68b.25-19513" "User Commands"
.SH NAME
autoheader \- Create a template header for configure
.SH SYNOPSIS
.B autoheader
[\fIOPTION\fR]... [\fITEMPLATE-FILE\fR]
.SH DESCRIPTION
Create a template file of C `#define' statements for `configure' to
use. To this end, scan TEMPLATE\-FILE, or `configure.ac' if present,
or else `configure.in'.
.TP
\fB\-h\fR, \fB\-\-help\fR
print this help, then exit
.TP
\fB\-V\fR, \fB\-\-version\fR
print version number, then exit
.TP
\fB\-v\fR, \fB\-\-verbose\fR
verbosely report processing
.TP
\fB\-d\fR, \fB\-\-debug\fR
don't remove temporary files
.TP
\fB\-f\fR, \fB\-\-force\fR
consider all files obsolete
.TP
\fB\-W\fR, \fB\-\-warnings\fR=\fICATEGORY\fR
report the warnings falling in CATEGORY
.SS "Warning categories include:"
.TP
`cross'
cross compilation issues
.TP
`gnu'
GNU coding standards (default in gnu and gnits modes)
.TP
`obsolete'
obsolete features or constructions
.TP
`override'
user redefinitions of Automake rules or variables
.TP
`portability'
portability issues (default in gnu and gnits modes)
.TP
`syntax'
dubious syntactic constructs (default)
.TP
`unsupported'
unsupported or incomplete features (default)
.TP
`all'
all the warnings
.TP
`no\-CATEGORY'
turn off warnings in CATEGORY
.TP
`none'
turn off all the warnings
.TP
`error'
treat warnings as errors
.SS "Library directories:"
.TP
\fB\-B\fR, \fB\-\-prepend\-include\fR=\fIDIR\fR
prepend directory DIR to search path
.TP
\fB\-I\fR, \fB\-\-include\fR=\fIDIR\fR
append directory DIR to search path
.SH AUTHOR
Written by Roland McGrath and Akim Demaille.
.SH "REPORTING BUGS"
Report bugs to .
.br
GNU Autoconf home page: .
.br
General help using GNU software: .
.SH COPYRIGHT
Copyright \(co 2012 Free Software Foundation, Inc.
License GPLv3+/Autoconf: GNU GPL version 3 or later
,
.br
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
.SH "SEE ALSO"
.BR autoconf (1),
.BR automake (1),
.BR autoreconf (1),
.BR autoupdate (1),
.BR autoheader (1),
.BR autoscan (1),
.BR config.guess (1),
.BR config.sub (1),
.BR ifnames (1),
.BR libtool (1).
.PP
The full documentation for
.B autoheader
is maintained as a Texinfo manual. If the
.B info
and
.B autoheader
programs are properly installed at your site, the command
.IP
.B info autoheader
.PP
should give you access to the complete manual.
0707010000cb8b000081a400000000000000000000000153156594000008230000011f00010018ffffffffffffffff0000002d00000000root/usr/local/share/man/man1/config.guess.1 .\" DO NOT MODIFY THIS FILE! It was generated by help2man 1.40.8.
.TH CONFIG.GUESS "1" "April 2012" "GNU Autoconf 2.68b.24-84e2" "User Commands"
.SH NAME
config.guess \- guess the build system triplet
.SH SYNOPSIS
.B config.guess
[\fIOPTION\fR]
.SH DESCRIPTION
The GNU build system distinguishes three types of machines, the
`build' machine on which the compilers are run, the `host' machine
on which the package being built will run, and, exclusively when you
build a compiler, assembler etc., the `target' machine, for which the
compiler being built will produce code.
This script will guess the type of the `build' machine.
.PP
Output the configuration name of the system `config.guess' is run on.
.SS "Operation modes:"
.TP
\fB\-h\fR, \fB\-\-help\fR
print this help, then exit
.TP
\fB\-t\fR, \fB\-\-time\-stamp\fR
print date of last modification, then exit
.TP
\fB\-v\fR, \fB\-\-version\fR
print version number, then exit
.SH "ENVIRONMENT VARIABLES"
config.guess might need to compile and run C code, hence it needs a
compiler for the `build' machine: use the environment variable
`CC_FOR_BUILD' to specify the compiler for the build machine. If
`CC_FOR_BUILD' is not specified, `CC' will be used. Be sure to
specify `CC_FOR_BUILD' is `CC' is a cross-compiler to the `host'
machine.
CC_FOR_BUILD a native C compiler, defaults to `cc'
CC a native C compiler, the previous variable is preferred
.SH "REPORTING BUGS"
Report bugs and patches to .
.PP
.br
Originally written by Per Bothner.
.br
Copyright \(co 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012
.br
Free Software Foundation, Inc.
.PP
.br
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
.SH "SEE ALSO"
.BR autoconf (1),
.BR automake (1),
.BR autoreconf (1),
.BR autoupdate (1),
.BR autoheader (1),
.BR autoscan (1),
.BR config.guess (1),
.BR config.sub (1),
.BR ifnames (1),
.BR libtool (1).
0707010000cb88000081a40000000000000000000000015315659400000dcf0000011f00010018ffffffffffffffff0000002b00000000root/usr/local/share/man/man1/autoreconf.1 .\" DO NOT MODIFY THIS FILE! It was generated by help2man 1.40.8.
.TH AUTORECONF "1" "April 2012" "GNU Autoconf 2.68b.22-280f-dirty" "User Commands"
.SH NAME
autoreconf \- Update generated configuration files
.SH SYNOPSIS
.B autoreconf
[\fIOPTION\fR]... [\fIDIRECTORY\fR]...
.SH DESCRIPTION
Run `autoconf' (and `autoheader', `aclocal', `automake', `autopoint'
(formerly `gettextize'), and `libtoolize' where appropriate)
repeatedly to remake the GNU Build System files in specified
DIRECTORIES and their subdirectories (defaulting to `.').
.PP
By default, it only remakes those files that are older than their
sources. If you install new versions of the GNU Build System,
you can make `autoreconf' remake all of the files by giving it the
`\-\-force' option.
.SS "Operation modes:"
.TP
\fB\-h\fR, \fB\-\-help\fR
print this help, then exit
.TP
\fB\-V\fR, \fB\-\-version\fR
print version number, then exit
.TP
\fB\-v\fR, \fB\-\-verbose\fR
verbosely report processing
.TP
\fB\-d\fR, \fB\-\-debug\fR
don't remove temporary files
.TP
\fB\-f\fR, \fB\-\-force\fR
consider all files obsolete
.TP
\fB\-i\fR, \fB\-\-install\fR
copy missing auxiliary files
.TP
\fB\-\-no\-recursive\fR
don't rebuild sub\-packages
.TP
\fB\-s\fR, \fB\-\-symlink\fR
with \fB\-i\fR, install symbolic links instead of copies
.TP
\fB\-m\fR, \fB\-\-make\fR
when applicable, re\-run ./configure && make
.TP
\fB\-W\fR, \fB\-\-warnings\fR=\fICATEGORY\fR
report the warnings falling in CATEGORY [syntax]
.SS "Warning categories include:"
.TP
`cross'
cross compilation issues
.TP
`gnu'
GNU coding standards (default in gnu and gnits modes)
.TP
`obsolete'
obsolete features or constructions
.TP
`override'
user redefinitions of Automake rules or variables
.TP
`portability'
portability issues (default in gnu and gnits modes)
.TP
`syntax'
dubious syntactic constructs (default)
.TP
`unsupported'
unsupported or incomplete features (default)
.TP
`all'
all the warnings
.TP
`no\-CATEGORY'
turn off warnings in CATEGORY
.TP
`none'
turn off all the warnings
.TP
`error'
treat warnings as errors
.PP
The environment variable `WARNINGS' is honored. Some subtools might
support other warning types, using `all' is encouraged.
.SS "Library directories:"
.TP
\fB\-B\fR, \fB\-\-prepend\-include\fR=\fIDIR\fR
prepend directory DIR to search path
.TP
\fB\-I\fR, \fB\-\-include\fR=\fIDIR\fR
append directory DIR to search path
.PP
The environment variables AUTOM4TE, AUTOCONF, AUTOHEADER, AUTOMAKE,
ACLOCAL, AUTOPOINT, LIBTOOLIZE, M4, and MAKE are honored.
.SH AUTHOR
Written by David J. MacKenzie and Akim Demaille.
.SH "REPORTING BUGS"
Report bugs to .
.br
GNU Autoconf home page: .
.br
General help using GNU software: .
.SH COPYRIGHT
Copyright \(co 2012 Free Software Foundation, Inc.
License GPLv3+/Autoconf: GNU GPL version 3 or later
,
.br
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
.SH "SEE ALSO"
.BR autoconf (1),
.BR automake (1),
.BR autoreconf (1),
.BR autoupdate (1),
.BR autoheader (1),
.BR autoscan (1),
.BR config.guess (1),
.BR config.sub (1),
.BR ifnames (1),
.BR libtool (1).
.PP
The full documentation for
.B autoreconf
is maintained as a Texinfo manual. If the
.B info
and
.B autoreconf
programs are properly installed at your site, the command
.IP
.B info autoreconf
.PP
should give you access to the complete manual.
0707010000cb89000081a400000000000000000000000153156594000007f00000011f00010018ffffffffffffffff0000002900000000root/usr/local/share/man/man1/autoscan.1 .\" DO NOT MODIFY THIS FILE! It was generated by help2man 1.40.8.
.TH AUTOSCAN "1" "April 2012" "GNU Autoconf 2.68b.25-19513" "User Commands"
.SH NAME
autoscan \- Generate a preliminary configure.in
.SH SYNOPSIS
.B autoscan
[\fIOPTION\fR]... [\fISRCDIR\fR]
.SH DESCRIPTION
Examine source files in the directory tree rooted at SRCDIR, or the
current directory if none is given. Search the source files for
common portability problems, check for incompleteness of
`configure.ac', and create a file `configure.scan' which is a
preliminary `configure.ac' for that package.
.TP
\fB\-h\fR, \fB\-\-help\fR
print this help, then exit
.TP
\fB\-V\fR, \fB\-\-version\fR
print version number, then exit
.TP
\fB\-v\fR, \fB\-\-verbose\fR
verbosely report processing
.TP
\fB\-d\fR, \fB\-\-debug\fR
don't remove temporary files
.SS "Library directories:"
.TP
\fB\-B\fR, \fB\-\-prepend\-include\fR=\fIDIR\fR
prepend directory DIR to search path
.TP
\fB\-I\fR, \fB\-\-include\fR=\fIDIR\fR
append directory DIR to search path
.SH AUTHOR
Written by David J. MacKenzie and Akim Demaille.
.SH "REPORTING BUGS"
Report bugs to .
.br
GNU Autoconf home page: .
.br
General help using GNU software: .
.SH COPYRIGHT
Copyright \(co 2012 Free Software Foundation, Inc.
License GPLv3+/Autoconf: GNU GPL version 3 or later
,
.br
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
.SH "SEE ALSO"
.BR autoconf (1),
.BR automake (1),
.BR autoreconf (1),
.BR autoupdate (1),
.BR autoheader (1),
.BR autoscan (1),
.BR config.guess (1),
.BR config.sub (1),
.BR ifnames (1),
.BR libtool (1).
.PP
The full documentation for
.B autoscan
is maintained as a Texinfo manual. If the
.B info
and
.B autoscan
programs are properly installed at your site, the command
.IP
.B info autoscan
.PP
should give you access to the complete manual.
0707010000cb8d000081a400000000000000000000000153156594000006e20000011f00010018ffffffffffffffff0000002800000000root/usr/local/share/man/man1/ifnames.1 .\" DO NOT MODIFY THIS FILE! It was generated by help2man 1.40.8.
.TH IFNAMES "1" "April 2012" "GNU Autoconf 2.68b.25-19513" "User Commands"
.SH NAME
ifnames \- Extract CPP conditionals from a set of files
.SH SYNOPSIS
.B ifnames
[\fIOPTION\fR]... [\fIFILE\fR]...
.SH DESCRIPTION
Scan all of the C source FILES (or the standard input, if none are
given) and write to the standard output a sorted list of all the
identifiers that appear in those files in `#if', `#elif', `#ifdef', or
`#ifndef' directives. Print each identifier on a line, followed by a
space\-separated list of the files in which that identifier occurs.
.TP
\fB\-h\fR, \fB\-\-help\fR
print this help, then exit
.TP
\fB\-V\fR, \fB\-\-version\fR
print version number, then exit
.SH AUTHOR
Written by David J. MacKenzie and Paul Eggert.
.SH "REPORTING BUGS"
Report bugs to .
.br
GNU Autoconf home page: .
.br
General help using GNU software: .
.SH COPYRIGHT
Copyright \(co 2012 Free Software Foundation, Inc.
License GPLv3+/Autoconf: GNU GPL version 3 or later
,
.br
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
.SH "SEE ALSO"
.BR autoconf (1),
.BR automake (1),
.BR autoreconf (1),
.BR autoupdate (1),
.BR autoheader (1),
.BR autoscan (1),
.BR config.guess (1),
.BR config.sub (1),
.BR ifnames (1),
.BR libtool (1).
.PP
The full documentation for
.B ifnames
is maintained as a Texinfo manual. If the
.B info
and
.B ifnames
programs are properly installed at your site, the command
.IP
.B info ifnames
.PP
should give you access to the complete manual.
0707010000cb85000081a40000000000000000000000015315659400000b540000011f00010018ffffffffffffffff0000002900000000root/usr/local/share/man/man1/autoconf.1 .\" DO NOT MODIFY THIS FILE! It was generated by help2man 1.40.6.
.TH AUTOCONF "1" "March 2012" "GNU Autoconf 2.68b" "User Commands"
.SH NAME
autoconf \- Generate configuration scripts
.SH SYNOPSIS
.B autoconf
[\fIOPTION\fR]... [\fITEMPLATE-FILE\fR]
.SH DESCRIPTION
Generate a configuration script from a TEMPLATE\-FILE if given, or
`configure.ac' if present, or else `configure.in'. Output is sent
to the standard output if TEMPLATE\-FILE is given, else into
`configure'.
.SS "Operation modes:"
.TP
\fB\-h\fR, \fB\-\-help\fR
print this help, then exit
.TP
\fB\-V\fR, \fB\-\-version\fR
print version number, then exit
.TP
\fB\-v\fR, \fB\-\-verbose\fR
verbosely report processing
.TP
\fB\-d\fR, \fB\-\-debug\fR
don't remove temporary files
.TP
\fB\-f\fR, \fB\-\-force\fR
consider all files obsolete
.TP
\fB\-o\fR, \fB\-\-output\fR=\fIFILE\fR
save output in FILE (stdout is the default)
.TP
\fB\-W\fR, \fB\-\-warnings\fR=\fICATEGORY\fR
report the warnings falling in CATEGORY [syntax]
.SS "Warning categories include:"
.TP
`cross'
cross compilation issues
.TP
`obsolete'
obsolete constructs
.TP
`syntax'
dubious syntactic constructs
.TP
`all'
all the warnings
.TP
`no\-CATEGORY'
turn off the warnings on CATEGORY
.TP
`none'
turn off all the warnings
.TP
`error'
warnings are error
.PP
The environment variables `M4' and `WARNINGS' are honored.
.SS "Library directories:"
.TP
\fB\-B\fR, \fB\-\-prepend\-include\fR=\fIDIR\fR
prepend directory DIR to search path
.TP
\fB\-I\fR, \fB\-\-include\fR=\fIDIR\fR
append directory DIR to search path
.SS "Tracing:"
.TP
\fB\-t\fR, \fB\-\-trace\fR=\fIMACRO[\fR:FORMAT]
report the list of calls to MACRO
.TP
\fB\-i\fR, \fB\-\-initialization\fR
also trace Autoconf's initialization process
.PP
In tracing mode, no configuration script is created. FORMAT defaults
to `$f:$l:$n:$%'; see `autom4te \fB\-\-help\fR' for information about FORMAT.
.SH AUTHOR
Written by David J. MacKenzie and Akim Demaille.
.SH "REPORTING BUGS"
Report bugs to .
.br
GNU Autoconf home page: .
.br
General help using GNU software: .
.SH COPYRIGHT
Copyright \(co 2012 Free Software Foundation, Inc.
License GPLv3+/Autoconf: GNU GPL version 3 or later
,
.br
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
.SH "SEE ALSO"
.BR autoconf (1),
.BR automake (1),
.BR autoreconf (1),
.BR autoupdate (1),
.BR autoheader (1),
.BR autoscan (1),
.BR config.guess (1),
.BR config.sub (1),
.BR ifnames (1),
.BR libtool (1).
.PP
The full documentation for
.B autoconf
is maintained as a Texinfo manual. If the
.B info
and
.B autoconf
programs are properly installed at your site, the command
.IP
.B info autoconf
.PP
should give you access to the complete manual.
0707010000cb7f000041ed0000000000000000000000025315661a000000000000011f00010018ffffffffffffffff0000001a00000000root/usr/local/share/info 0707010000cb82000081a4000000000000000000000001531565930003777f0000011f00010018ffffffffffffffff0000002900000000root/usr/local/share/info/standards.info This is standards.info, produced by makeinfo version 4.13 from
standards.texi.
INFO-DIR-SECTION GNU organization
START-INFO-DIR-ENTRY
* Standards: (standards). GNU coding standards.
END-INFO-DIR-ENTRY
The GNU coding standards, last updated April 7, 2012.
Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012
Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts. A copy of the license is included in the section entitled "GNU
Free Documentation License".
File: standards.info, Node: Top, Next: Preface, Up: (dir)
GNU Coding Standards
********************
The GNU coding standards, last updated April 7, 2012.
Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012
Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts. A copy of the license is included in the section entitled "GNU
Free Documentation License".
* Menu:
* Preface:: About the GNU Coding Standards.
* Legal Issues:: Keeping free software free.
* Design Advice:: General program design.
* Program Behavior:: Program behavior for all programs
* Writing C:: Making the best use of C.
* Documentation:: Documenting programs.
* Managing Releases:: The release process.
* References:: Mentioning non-free software or documentation.
* GNU Free Documentation License:: Copying and sharing this manual.
* Index::
File: standards.info, Node: Preface, Next: Legal Issues, Prev: Top, Up: Top
1 About the GNU Coding Standards
********************************
The GNU Coding Standards were written by Richard Stallman and other GNU
Project volunteers. Their purpose is to make the GNU system clean,
consistent, and easy to install. This document can also be read as a
guide to writing portable, robust and reliable programs. It focuses on
programs written in C, but many of the rules and principles are useful
even if you write in another programming language. The rules often
state reasons for writing in a certain way.
If you did not obtain this file directly from the GNU project and
recently, please check for a newer version. You can get the GNU Coding
Standards from the GNU web server in many different formats, including
the Texinfo source, PDF, HTML, DVI, plain text, and more, at:
`http://www.gnu.org/prep/standards/'.
If you are maintaining an official GNU package, in addition to this
document, please read and follow the GNU maintainer information (*note
Contents: (maintain)Top.).
If you want to receive diffs for every change to these GNU documents,
join the mailing list `gnustandards-commit@gnu.org', via the web
interface at
`http://lists.gnu.org/mailman/listinfo/gnustandards-commit'. Archives
are also available there.
Please send corrections or suggestions for this document to
. If you make a suggestion, please include a
suggested new wording for it, to help us consider the suggestion
efficiently. We prefer a context diff to the Texinfo source, but if
that's difficult for you, you can make a context diff for some other
version of this document, or propose it in any way that makes it clear.
The source repository for this document can be found at
`http://savannah.gnu.org/projects/gnustandards'.
These standards cover the minimum of what is important when writing a
GNU package. Likely, the need for additional standards will come up.
Sometimes, you might suggest that such standards be added to this
document. If you think your standards would be generally useful, please
do suggest them.
You should also set standards for your package on many questions not
addressed or not firmly specified here. The most important point is to
be self-consistent--try to stick to the conventions you pick, and try
to document them as much as possible. That way, your program will be
more maintainable by others.
The GNU Hello program serves as an example of how to follow the GNU
coding standards for a trivial program.
`http://www.gnu.org/software/hello/hello.html'.
This release of the GNU Coding Standards was last updated April 7,
2012.
File: standards.info, Node: Legal Issues, Next: Design Advice, Prev: Preface, Up: Top
2 Keeping Free Software Free
****************************
This chapter discusses how you can make sure that GNU software avoids
legal difficulties, and other related issues.
* Menu:
* Reading Non-Free Code:: Referring to proprietary programs.
* Contributions:: Accepting contributions.
* Trademarks:: How we deal with trademark issues.
File: standards.info, Node: Reading Non-Free Code, Next: Contributions, Up: Legal Issues
2.1 Referring to Proprietary Programs
=====================================
Don't in any circumstances refer to Unix source code for or during your
work on GNU! (Or to any other proprietary programs.)
If you have a vague recollection of the internals of a Unix program,
this does not absolutely mean you can't write an imitation of it, but
do try to organize the imitation internally along different lines,
because this is likely to make the details of the Unix version
irrelevant and dissimilar to your results.
For example, Unix utilities were generally optimized to minimize
memory use; if you go for speed instead, your program will be very
different. You could keep the entire input file in memory and scan it
there instead of using stdio. Use a smarter algorithm discovered more
recently than the Unix program. Eliminate use of temporary files. Do
it in one pass instead of two (we did this in the assembler).
Or, on the contrary, emphasize simplicity instead of speed. For some
applications, the speed of today's computers makes simpler algorithms
adequate.
Or go for generality. For example, Unix programs often have static
tables or fixed-size strings, which make for arbitrary limits; use
dynamic allocation instead. Make sure your program handles NULs and
other funny characters in the input files. Add a programming language
for extensibility and write part of the program in that language.
Or turn some parts of the program into independently usable
libraries. Or use a simple garbage collector instead of tracking
precisely when to free memory, or use a new GNU facility such as
obstacks.
File: standards.info, Node: Contributions, Next: Trademarks, Prev: Reading Non-Free Code, Up: Legal Issues
2.2 Accepting Contributions
===========================
If the program you are working on is copyrighted by the Free Software
Foundation, then when someone else sends you a piece of code to add to
the program, we need legal papers to use it--just as we asked you to
sign papers initially. _Each_ person who makes a nontrivial
contribution to a program must sign some sort of legal papers in order
for us to have clear title to the program; the main author alone is not
enough.
So, before adding in any contributions from other people, please tell
us, so we can arrange to get the papers. Then wait until we tell you
that we have received the signed papers, before you actually use the
contribution.
This applies both before you release the program and afterward. If
you receive diffs to fix a bug, and they make significant changes, we
need legal papers for that change.
This also applies to comments and documentation files. For copyright
law, comments and code are just text. Copyright applies to all kinds of
text, so we need legal papers for all kinds.
We know it is frustrating to ask for legal papers; it's frustrating
for us as well. But if you don't wait, you are going out on a limb--for
example, what if the contributor's employer won't sign a disclaimer?
You might have to take that code out again!
You don't need papers for changes of a few lines here or there, since
they are not significant for copyright purposes. Also, you don't need
papers if all you get from the suggestion is some ideas, not actual code
which you use. For example, if someone sent you one implementation, but
you write a different implementation of the same idea, you don't need to
get papers.
The very worst thing is if you forget to tell us about the other
contributor. We could be very embarrassed in court some day as a
result.
We have more detailed advice for maintainers of GNU packages. If you
have reached the stage of maintaining a GNU program (whether released
or not), please take a look: *note Legal Matters: (maintain)Legal
Matters.
File: standards.info, Node: Trademarks, Prev: Contributions, Up: Legal Issues
2.3 Trademarks
==============
Please do not include any trademark acknowledgements in GNU software
packages or documentation.
Trademark acknowledgements are the statements that such-and-such is a
trademark of so-and-so. The GNU Project has no objection to the basic
idea of trademarks, but these acknowledgements feel like kowtowing, and
there is no legal requirement for them, so we don't use them.
What is legally required, as regards other people's trademarks, is to
avoid using them in ways which a reader might reasonably understand as
naming or labeling our own programs or activities. For example, since
"Objective C" is (or at least was) a trademark, we made sure to say
that we provide a "compiler for the Objective C language" rather than
an "Objective C compiler". The latter would have been meant as a
shorter way of saying the former, but it does not explicitly state the
relationship, so it could be misinterpreted as using "Objective C" as a
label for the compiler rather than for the language.
Please don't use "win" as an abbreviation for Microsoft Windows in
GNU software or documentation. In hacker terminology, calling
something a "win" is a form of praise. If you wish to praise Microsoft
Windows when speaking on your own, by all means do so, but not in GNU
software. Usually we write the name "Windows" in full, but when
brevity is very important (as in file names and sometimes symbol
names), we abbreviate it to "w". For instance, the files and functions
in Emacs that deal with Windows start with `w32'.
File: standards.info, Node: Design Advice, Next: Program Behavior, Prev: Legal Issues, Up: Top
3 General Program Design
************************
This chapter discusses some of the issues you should take into account
when designing your program.
* Menu:
* Source Language:: Which languages to use.
* Compatibility:: Compatibility with other implementations.
* Using Extensions:: Using non-standard features.
* Standard C:: Using standard C features.
* Conditional Compilation:: Compiling code only if a conditional is true.
File: standards.info, Node: Source Language, Next: Compatibility, Up: Design Advice
3.1 Which Languages to Use
==========================
When you want to use a language that gets compiled and runs at high
speed, the best language to use is C. Using another language is like
using a non-standard feature: it will cause trouble for users. Even if
GCC supports the other language, users may find it inconvenient to have
to install the compiler for that other language in order to build your
program. For example, if you write your program in C++, people will
have to install the GNU C++ compiler in order to compile your program.
C has one other advantage over C++ and other compiled languages: more
people know C, so more people will find it easy to read and modify the
program if it is written in C.
So in general it is much better to use C, rather than the comparable
alternatives.
But there are two exceptions to that conclusion:
* It is no problem to use another language to write a tool
specifically intended for use with that language. That is because
the only people who want to build the tool will be those who have
installed the other language anyway.
* If an application is of interest only to a narrow part of the
community, then the question of which language it is written in
has less effect on other people, so you may as well please
yourself.
Many programs are designed to be extensible: they include an
interpreter for a language that is higher level than C. Often much of
the program is written in that language, too. The Emacs editor
pioneered this technique.
The standard extensibility interpreter for GNU software is Guile
(`http://www.gnu.org/software/guile/'), which implements the language
Scheme (an especially clean and simple dialect of Lisp). Guile also
includes bindings for GTK+/GNOME, making it practical to write modern
GUI functionality within Guile. We don't reject programs written in
other "scripting languages" such as Perl and Python, but using Guile is
very important for the overall consistency of the GNU system.
File: standards.info, Node: Compatibility, Next: Using Extensions, Prev: Source Language, Up: Design Advice
3.2 Compatibility with Other Implementations
============================================
With occasional exceptions, utility programs and libraries for GNU
should be upward compatible with those in Berkeley Unix, and upward
compatible with Standard C if Standard C specifies their behavior, and
upward compatible with POSIX if POSIX specifies their behavior.
When these standards conflict, it is useful to offer compatibility
modes for each of them.
Standard C and POSIX prohibit many kinds of extensions. Feel free
to make the extensions anyway, and include a `--ansi', `--posix', or
`--compatible' option to turn them off. However, if the extension has
a significant chance of breaking any real programs or scripts, then it
is not really upward compatible. So you should try to redesign its
interface to make it upward compatible.
Many GNU programs suppress extensions that conflict with POSIX if the
environment variable `POSIXLY_CORRECT' is defined (even if it is
defined with a null value). Please make your program recognize this
variable if appropriate.
When a feature is used only by users (not by programs or command
files), and it is done poorly in Unix, feel free to replace it
completely with something totally different and better. (For example,
`vi' is replaced with Emacs.) But it is nice to offer a compatible
feature as well. (There is a free `vi' clone, so we offer it.)
Additional useful features are welcome regardless of whether there
is any precedent for them.
File: standards.info, Node: Using Extensions, Next: Standard C, Prev: Compatibility, Up: Design Advice
3.3 Using Non-standard Features
===============================
Many GNU facilities that already exist support a number of convenient
extensions over the comparable Unix facilities. Whether to use these
extensions in implementing your program is a difficult question.
On the one hand, using the extensions can make a cleaner program.
On the other hand, people will not be able to build the program unless
the other GNU tools are available. This might cause the program to
work on fewer kinds of machines.
With some extensions, it might be easy to provide both alternatives.
For example, you can define functions with a "keyword" `INLINE' and
define that as a macro to expand into either `inline' or nothing,
depending on the compiler.
In general, perhaps it is best not to use the extensions if you can
straightforwardly do without them, but to use the extensions if they
are a big improvement.
An exception to this rule are the large, established programs (such
as Emacs) which run on a great variety of systems. Using GNU
extensions in such programs would make many users unhappy, so we don't
do that.
Another exception is for programs that are used as part of
compilation: anything that must be compiled with other compilers in
order to bootstrap the GNU compilation facilities. If these require
the GNU compiler, then no one can compile them without having them
installed already. That would be extremely troublesome in certain
cases.
File: standards.info, Node: Standard C, Next: Conditional Compilation, Prev: Using Extensions, Up: Design Advice
3.4 Standard C and Pre-Standard C
=================================
1989 Standard C is widespread enough now that it is ok to use its
features in new programs. There is one exception: do not ever use the
"trigraph" feature of Standard C.
1999 Standard C is not widespread yet, so please do not require its
features in programs. It is ok to use its features if they are present.
However, it is easy to support pre-standard compilers in most
programs, so if you know how to do that, feel free. If a program you
are maintaining has such support, you should try to keep it working.
To support pre-standard C, instead of writing function definitions in
standard prototype form,
int
foo (int x, int y)
...
write the definition in pre-standard style like this,
int
foo (x, y)
int x, y;
...
and use a separate declaration to specify the argument prototype:
int foo (int, int);
You need such a declaration anyway, in a header file, to get the
benefit of prototypes in all the files where the function is called.
And once you have the declaration, you normally lose nothing by writing
the function definition in the pre-standard style.
This technique does not work for integer types narrower than `int'.
If you think of an argument as being of a type narrower than `int',
declare it as `int' instead.
There are a few special cases where this technique is hard to use.
For example, if a function argument needs to hold the system type
`dev_t', you run into trouble, because `dev_t' is shorter than `int' on
some machines; but you cannot use `int' instead, because `dev_t' is
wider than `int' on some machines. There is no type you can safely use
on all machines in a non-standard definition. The only way to support
non-standard C and pass such an argument is to check the width of
`dev_t' using Autoconf and choose the argument type accordingly. This
may not be worth the trouble.
In order to support pre-standard compilers that do not recognize
prototypes, you may want to use a preprocessor macro like this:
/* Declare the prototype for a general external function. */
#if defined (__STDC__) || defined (WINDOWSNT)
#define P_(proto) proto
#else
#define P_(proto) ()
#endif
File: standards.info, Node: Conditional Compilation, Prev: Standard C, Up: Design Advice
3.5 Conditional Compilation
===========================
When supporting configuration options already known when building your
program we prefer using `if (... )' over conditional compilation, as in
the former case the compiler is able to perform more extensive checking
of all possible code paths.
For example, please write
if (HAS_FOO)
...
else
...
instead of:
#ifdef HAS_FOO
...
#else
...
#endif
A modern compiler such as GCC will generate exactly the same code in
both cases, and we have been using similar techniques with good success
in several projects. Of course, the former method assumes that
`HAS_FOO' is defined as either 0 or 1.
While this is not a silver bullet solving all portability problems,
and is not always appropriate, following this policy would have saved
GCC developers many hours, or even days, per year.
In the case of function-like macros like `REVERSIBLE_CC_MODE' in GCC
which cannot be simply used in `if (...)' statements, there is an easy
workaround. Simply introduce another macro `HAS_REVERSIBLE_CC_MODE' as
in the following example:
#ifdef REVERSIBLE_CC_MODE
#define HAS_REVERSIBLE_CC_MODE 1
#else
#define HAS_REVERSIBLE_CC_MODE 0
#endif
File: standards.info, Node: Program Behavior, Next: Writing C, Prev: Design Advice, Up: Top
4 Program Behavior for All Programs
***********************************
This chapter describes conventions for writing robust software. It
also describes general standards for error messages, the command line
interface, and how libraries should behave.
* Menu:
* Non-GNU Standards:: We consider standards such as POSIX;
we don't "obey" them.
* Semantics:: Writing robust programs.
* Libraries:: Library behavior.
* Errors:: Formatting error messages.
* User Interfaces:: Standards about interfaces generally.
* Graphical Interfaces:: Standards for graphical interfaces.
* Command-Line Interfaces:: Standards for command line interfaces.
* Dynamic Plug-In Interfaces:: Standards for dynamic plug-in interfaces.
* Option Table:: Table of long options.
* OID Allocations:: Table of OID slots for GNU.
* Memory Usage:: When and how to care about memory needs.
* File Usage:: Which files to use, and where.
File: standards.info, Node: Non-GNU Standards, Next: Semantics, Up: Program Behavior
4.1 Non-GNU Standards
=====================
The GNU Project regards standards published by other organizations as
suggestions, not orders. We consider those standards, but we do not
"obey" them. In developing a GNU program, you should implement an
outside standard's specifications when that makes the GNU system better
overall in an objective sense. When it doesn't, you shouldn't.
In most cases, following published standards is convenient for
users--it means that their programs or scripts will work more portably.
For instance, GCC implements nearly all the features of Standard C as
specified by that standard. C program developers would be unhappy if
it did not. And GNU utilities mostly follow specifications of POSIX.2;
shell script writers and users would be unhappy if our programs were
incompatible.
But we do not follow either of these specifications rigidly, and
there are specific points on which we decided not to follow them, so as
to make the GNU system better for users.
For instance, Standard C says that nearly all extensions to C are
prohibited. How silly! GCC implements many extensions, some of which
were later adopted as part of the standard. If you want these
constructs to give an error message as "required" by the standard, you
must specify `--pedantic', which was implemented only so that we can
say "GCC is a 100% implementation of the standard", not because there
is any reason to actually use it.
POSIX.2 specifies that `df' and `du' must output sizes by default in
units of 512 bytes. What users want is units of 1k, so that is what we
do by default. If you want the ridiculous behavior "required" by
POSIX, you must set the environment variable `POSIXLY_CORRECT' (which
was originally going to be named `POSIX_ME_HARDER').
GNU utilities also depart from the letter of the POSIX.2
specification when they support long-named command-line options, and
intermixing options with ordinary arguments. This minor
incompatibility with POSIX is never a problem in practice, and it is
very useful.
In particular, don't reject a new feature, or remove an old one,
merely because a standard says it is "forbidden" or "deprecated".
File: standards.info, Node: Semantics, Next: Libraries, Prev: Non-GNU Standards, Up: Program Behavior
4.2 Writing Robust Programs
===========================
Avoid arbitrary limits on the length or number of _any_ data structure,
including file names, lines, files, and symbols, by allocating all data
structures dynamically. In most Unix utilities, "long lines are
silently truncated". This is not acceptable in a GNU utility.
Utilities reading files should not drop NUL characters, or any other
nonprinting characters _including those with codes above 0177_. The
only sensible exceptions would be utilities specifically intended for
interface to certain types of terminals or printers that can't handle
those characters. Whenever possible, try to make programs work
properly with sequences of bytes that represent multibyte characters;
UTF-8 is the most important.
Check every system call for an error return, unless you know you wish
to ignore errors. Include the system error text (from `perror',
`strerror', or equivalent) in _every_ error message resulting from a
failing system call, as well as the name of the file if any and the
name of the utility. Just "cannot open foo.c" or "stat failed" is not
sufficient.
Check every call to `malloc' or `realloc' to see if it returned
zero. Check `realloc' even if you are making the block smaller; in a
system that rounds block sizes to a power of 2, `realloc' may get a
different block if you ask for less space.
In Unix, `realloc' can destroy the storage block if it returns zero.
GNU `realloc' does not have this bug: if it fails, the original block
is unchanged. Feel free to assume the bug is fixed. If you wish to
run your program on Unix, and wish to avoid lossage in this case, you
can use the GNU `malloc'.
You must expect `free' to alter the contents of the block that was
freed. Anything you want to fetch from the block, you must fetch before
calling `free'.
If `malloc' fails in a noninteractive program, make that a fatal
error. In an interactive program (one that reads commands from the
user), it is better to abort the command and return to the command
reader loop. This allows the user to kill other processes to free up
virtual memory, and then try the command again.
Use `getopt_long' to decode arguments, unless the argument syntax
makes this unreasonable.
When static storage is to be written in during program execution, use
explicit C code to initialize it. Reserve C initialized declarations
for data that will not be changed.
Try to avoid low-level interfaces to obscure Unix data structures
(such as file directories, utmp, or the layout of kernel memory), since
these are less likely to work compatibly. If you need to find all the
files in a directory, use `readdir' or some other high-level interface.
These are supported compatibly by GNU.
The preferred signal handling facilities are the BSD variant of
`signal', and the POSIX `sigaction' function; the alternative USG
`signal' interface is an inferior design.
Nowadays, using the POSIX signal functions may be the easiest way to
make a program portable. If you use `signal', then on GNU/Linux
systems running GNU libc version 1, you should include `bsd/signal.h'
instead of `signal.h', so as to get BSD behavior. It is up to you
whether to support systems where `signal' has only the USG behavior, or
give up on them.
In error checks that detect "impossible" conditions, just abort.
There is usually no point in printing any message. These checks
indicate the existence of bugs. Whoever wants to fix the bugs will have
to read the source code and run a debugger. So explain the problem with
comments in the source. The relevant data will be in variables, which
are easy to examine with the debugger, so there is no point moving them
elsewhere.
Do not use a count of errors as the exit status for a program.
_That does not work_, because exit status values are limited to 8 bits
(0 through 255). A single run of the program might have 256 errors; if
you try to return 256 as the exit status, the parent process will see 0
as the status, and it will appear that the program succeeded.
If you make temporary files, check the `TMPDIR' environment
variable; if that variable is defined, use the specified directory
instead of `/tmp'.
In addition, be aware that there is a possible security problem when
creating temporary files in world-writable directories. In C, you can
avoid this problem by creating temporary files in this manner:
fd = open (filename, O_WRONLY | O_CREAT | O_EXCL, 0600);
or by using the `mkstemps' function from Gnulib (*note mkstemps:
(gnulib)mkstemps.).
In bash, use `set -C' (long name `noclobber') to avoid this problem.
In addition, the `mktemp' utility is a more general solution for
creating temporary files from shell scripts (*note mktemp invocation:
(coreutils)mktemp invocation.).
File: standards.info, Node: Libraries, Next: Errors, Prev: Semantics, Up: Program Behavior
4.3 Library Behavior
====================
Try to make library functions reentrant. If they need to do dynamic
storage allocation, at least try to avoid any nonreentrancy aside from
that of `malloc' itself.
Here are certain name conventions for libraries, to avoid name
conflicts.
Choose a name prefix for the library, more than two characters long.
All external function and variable names should start with this prefix.
In addition, there should only be one of these in any given library
member. This usually means putting each one in a separate source file.
An exception can be made when two external symbols are always used
together, so that no reasonable program could use one without the
other; then they can both go in the same file.
External symbols that are not documented entry points for the user
should have names beginning with `_'. The `_' should be followed by
the chosen name prefix for the library, to prevent collisions with
other libraries. These can go in the same files with user entry points
if you like.
Static functions and variables can be used as you like and need not
fit any naming convention.
File: standards.info, Node: Errors, Next: User Interfaces, Prev: Libraries, Up: Program Behavior
4.4 Formatting Error Messages
=============================
Error messages from compilers should look like this:
SOURCEFILE:LINENO: MESSAGE
If you want to mention the column number, use one of these formats:
SOURCEFILE:LINENO:COLUMN: MESSAGE
SOURCEFILE:LINENO.COLUMN: MESSAGE
Line numbers should start from 1 at the beginning of the file, and
column numbers should start from 1 at the beginning of the line. (Both
of these conventions are chosen for compatibility.) Calculate column
numbers assuming that space and all ASCII printing characters have
equal width, and assuming tab stops every 8 columns. For non-ASCII
characters, Unicode character widths should be used when in a UTF-8
locale; GNU libc and GNU gnulib provide suitable `wcwidth' functions.
The error message can also give both the starting and ending
positions of the erroneous text. There are several formats so that you
can avoid redundant information such as a duplicate line number. Here
are the possible formats:
SOURCEFILE:LINE1.COLUMN1-LINE2.COLUMN2: MESSAGE
SOURCEFILE:LINE1.COLUMN1-COLUMN2: MESSAGE
SOURCEFILE:LINE1-LINE2: MESSAGE
When an error is spread over several files, you can use this format:
FILE1:LINE1.COLUMN1-FILE2:LINE2.COLUMN2: MESSAGE
Error messages from other noninteractive programs should look like
this:
PROGRAM:SOURCEFILE:LINENO: MESSAGE
when there is an appropriate source file, or like this:
PROGRAM: MESSAGE
when there is no relevant source file.
If you want to mention the column number, use this format:
PROGRAM:SOURCEFILE:LINENO:COLUMN: MESSAGE
In an interactive program (one that is reading commands from a
terminal), it is better not to include the program name in an error
message. The place to indicate which program is running is in the
prompt or with the screen layout. (When the same program runs with
input from a source other than a terminal, it is not interactive and
would do best to print error messages using the noninteractive style.)
The string MESSAGE should not begin with a capital letter when it
follows a program name and/or file name, because that isn't the
beginning of a sentence. (The sentence conceptually starts at the
beginning of the line.) Also, it should not end with a period.
Error messages from interactive programs, and other messages such as
usage messages, should start with a capital letter. But they should not
end with a period.
File: standards.info, Node: User Interfaces, Next: Graphical Interfaces, Prev: Errors, Up: Program Behavior
4.5 Standards for Interfaces Generally
======================================
Please don't make the behavior of a utility depend on the name used to
invoke it. It is useful sometimes to make a link to a utility with a
different name, and that should not change what it does.
Instead, use a run time option or a compilation switch or both to
select among the alternate behaviors.
Likewise, please don't make the behavior of the program depend on the
type of output device it is used with. Device independence is an
important principle of the system's design; do not compromise it merely
to save someone from typing an option now and then. (Variation in error
message syntax when using a terminal is ok, because that is a side issue
that people do not depend on.)
If you think one behavior is most useful when the output is to a
terminal, and another is most useful when the output is a file or a
pipe, then it is usually best to make the default behavior the one that
is useful with output to a terminal, and have an option for the other
behavior.
Compatibility requires certain programs to depend on the type of
output device. It would be disastrous if `ls' or `sh' did not do so in
the way all users expect. In some of these cases, we supplement the
program with a preferred alternate version that does not depend on the
output device type. For example, we provide a `dir' program much like
`ls' except that its default output format is always multi-column
format.
File: standards.info, Node: Graphical Interfaces, Next: Command-Line Interfaces, Prev: User Interfaces, Up: Program Behavior
4.6 Standards for Graphical Interfaces
======================================
When you write a program that provides a graphical user interface,
please make it work with the X Window System and the GTK+ toolkit
unless the functionality specifically requires some alternative (for
example, "displaying jpeg images while in console mode").
In addition, please provide a command-line interface to control the
functionality. (In many cases, the graphical user interface can be a
separate program which invokes the command-line program.) This is so
that the same jobs can be done from scripts.
Please also consider providing a D-bus interface for use from other
running programs, such as within GNOME. (GNOME used to use CORBA for
this, but that is being phased out.) In addition, consider providing a
library interface (for use from C), and perhaps a keyboard-driven
console interface (for use by users from console mode). Once you are
doing the work to provide the functionality and the graphical
interface, these won't be much extra work.
File: standards.info, Node: Command-Line Interfaces, Next: Dynamic Plug-In Interfaces, Prev: Graphical Interfaces, Up: Program Behavior
4.7 Standards for Command Line Interfaces
=========================================
It is a good idea to follow the POSIX guidelines for the command-line
options of a program. The easiest way to do this is to use `getopt' to
parse them. Note that the GNU version of `getopt' will normally permit
options anywhere among the arguments unless the special argument `--'
is used. This is not what POSIX specifies; it is a GNU extension.
Please define long-named options that are equivalent to the
single-letter Unix-style options. We hope to make GNU more user
friendly this way. This is easy to do with the GNU function
`getopt_long'.
One of the advantages of long-named options is that they can be
consistent from program to program. For example, users should be able
to expect the "verbose" option of any GNU program which has one, to be
spelled precisely `--verbose'. To achieve this uniformity, look at the
table of common long-option names when you choose the option names for
your program (*note Option Table::).
It is usually a good idea for file names given as ordinary arguments
to be input files only; any output files would be specified using
options (preferably `-o' or `--output'). Even if you allow an output
file name as an ordinary argument for compatibility, try to provide an
option as another way to specify it. This will lead to more consistency
among GNU utilities, and fewer idiosyncrasies for users to remember.
All programs should support two standard options: `--version' and
`--help'. CGI programs should accept these as command-line options,
and also if given as the `PATH_INFO'; for instance, visiting
`http://example.org/p.cgi/--help' in a browser should output the same
information as invoking `p.cgi --help' from the command line.
* Menu:
* --version:: The standard output for --version.
* --help:: The standard output for --help.
File: standards.info, Node: --version, Next: --help, Up: Command-Line Interfaces
4.7.1 `--version'
-----------------
The standard `--version' option should direct the program to print
information about its name, version, origin and legal status, all on
standard output, and then exit successfully. Other options and
arguments should be ignored once this is seen, and the program should
not perform its normal function.
The first line is meant to be easy for a program to parse; the
version number proper starts after the last space. In addition, it
contains the canonical name for this program, in this format:
GNU Emacs 19.30
The program's name should be a constant string; _don't_ compute it from
`argv[0]'. The idea is to state the standard or canonical name for the
program, not its file name. There are other ways to find out the
precise file name where a command is found in `PATH'.
If the program is a subsidiary part of a larger package, mention the
package name in parentheses, like this:
emacsserver (GNU Emacs) 19.30
If the package has a version number which is different from this
program's version number, you can mention the package version number
just before the close-parenthesis.
If you _need_ to mention the version numbers of libraries which are
distributed separately from the package which contains this program,
you can do so by printing an additional line of version info for each
library you want to mention. Use the same format for these lines as for
the first line.
Please do not mention all of the libraries that the program uses
"just for completeness"--that would produce a lot of unhelpful clutter.
Please mention library version numbers only if you find in practice that
they are very important to you in debugging.
The following line, after the version number line or lines, should
be a copyright notice. If more than one copyright notice is called
for, put each on a separate line.
Next should follow a line stating the license, preferably using one
of abbreviations below, and a brief statement that the program is free
software, and that users are free to copy and change it. Also mention
that there is no warranty, to the extent permitted by law. See
recommended wording below.
It is ok to finish the output with a list of the major authors of the
program, as a way of giving credit.
Here's an example of output that follows these rules:
GNU hello 2.3
Copyright (C) 2007 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
You should adapt this to your program, of course, filling in the
proper year, copyright holder, name of program, and the references to
distribution terms, and changing the rest of the wording as necessary.
This copyright notice only needs to mention the most recent year in
which changes were made--there's no need to list the years for previous
versions' changes. You don't have to mention the name of the program in
these notices, if that is inconvenient, since it appeared in the first
line. (The rules are different for copyright notices in source files;
*note Copyright Notices: (maintain)Copyright Notices.)
Translations of the above lines must preserve the validity of the
copyright notices (*note Internationalization::). If the translation's
character set supports it, the `(C)' should be replaced with the
copyright symbol, as follows:
(the official copyright symbol, which is the letter C in a circle);
Write the word "Copyright" exactly like that, in English. Do not
translate it into another language. International treaties recognize
the English word "Copyright"; translations into other languages do not
have legal significance.
Finally, here is the table of our suggested license abbreviations.
Any abbreviation can be followed by `vVERSION[+]', meaning that
particular version, or later versions with the `+', as shown above.
In the case of exceptions for extra permissions with the GPL, we use
`/' for a separator; the version number can follow the license
abbreviation as usual, as in the examples below.
GPL
GNU General Public License, `http://www.gnu.org/licenses/gpl.html'.
LGPL
GNU Lesser General Public License,
`http://www.gnu.org/licenses/lgpl.html'.
GPL/Ada
GNU GPL with the exception for Ada.
Apache
The Apache Software Foundation license,
`http://www.apache.org/licenses'.
Artistic
The Artistic license used for Perl,
`http://www.perlfoundation.org/legal'.
Expat
The Expat license, `http://www.jclark.com/xml/copying.txt'.
MPL
The Mozilla Public License, `http://www.mozilla.org/MPL/'.
OBSD
The original (4-clause) BSD license, incompatible with the GNU GPL
`http://www.xfree86.org/3.3.6/COPYRIGHT2.html#6'.
PHP
The license used for PHP, `http://www.php.net/license/'.
public domain
The non-license that is being in the public domain,
`http://www.gnu.org/licenses/license-list.html#PublicDomain'.
Python
The license for Python, `http://www.python.org/2.0.1/license.html'.
RBSD
The revised (3-clause) BSD, compatible with the GNU GPL,
`http://www.xfree86.org/3.3.6/COPYRIGHT2.html#5'.
X11
The simple non-copyleft license used for most versions of the X
Window System, `http://www.xfree86.org/3.3.6/COPYRIGHT2.html#3'.
Zlib
The license for Zlib, `http://www.gzip.org/zlib/zlib_license.html'.
More information about these licenses and many more are on the GNU
licensing web pages, `http://www.gnu.org/licenses/license-list.html'.
File: standards.info, Node: --help, Prev: --version, Up: Command-Line Interfaces
4.7.2 `--help'
--------------
The standard `--help' option should output brief documentation for how
to invoke the program, on standard output, then exit successfully.
Other options and arguments should be ignored once this is seen, and
the program should not perform its normal function.
Near the end of the `--help' option's output, please place lines
giving the email address for bug reports, the package's home page
(normally , and the general page for
help using GNU programs. The format should be like this:
Report bugs to: MAILING-ADDRESS
PKG home page:
General help using GNU software:
It is ok to mention other appropriate mailing lists and web pages.
File: standards.info, Node: Dynamic Plug-In Interfaces, Next: Option Table, Prev: Command-Line Interfaces, Up: Program Behavior
4.8 Standards for Dynamic Plug-in Interfaces
============================================
Another aspect of keeping free programs free is encouraging development
of free plug-ins, and discouraging development of proprietary plug-ins.
Many GNU programs will not have anything like plug-ins at all, but
those that do should follow these practices.
First, the general plug-in architecture design should closely tie the
plug-in to the original code, such that the plug-in and the base
program are parts of one extended program. For GCC, for example,
plug-ins receive and modify GCC's internal data structures, and so
clearly form an extended program with the base GCC.
Second, you should require plug-in developers to affirm that their
plug-ins are released under an appropriate license. This should be
enforced with a simple programmatic check. For GCC, again for example,
a plug-in must define the global symbol `plugin_is_GPL_compatible',
thus asserting that the plug-in is released under a GPL-compatible
license (*note Plugins: (gccint)Plugins.).
By adding this check to your program you are not creating a new legal
requirement. The GPL itself requires plug-ins to be free software,
licensed compatibly. As long as you have followed the first rule above
to keep plug-ins closely tied to your original program, the GPL and AGPL
already require those plug-ins to be released under a compatible
license. The symbol definition in the plug-in--or whatever equivalent
works best in your program--makes it harder for anyone who might
distribute proprietary plug-ins to legally defend themselves. If a case
about this got to court, we can point to that symbol as evidence that
the plug-in developer understood that the license had this requirement.
File: standards.info, Node: Option Table, Next: OID Allocations, Prev: Dynamic Plug-In Interfaces, Up: Program Behavior
4.9 Table of Long Options
=========================
Here is a table of long options used by GNU programs. It is surely
incomplete, but we aim to list all the options that a new program might
want to be compatible with. If you use names not already in the table,
please send a list of them, with their
meanings, so we can update the table.
`after-date'
`-N' in `tar'.
`all'
`-a' in `du', `ls', `nm', `stty', `uname', and `unexpand'.
`all-text'
`-a' in `diff'.
`almost-all'
`-A' in `ls'.
`append'
`-a' in `etags', `tee', `time'; `-r' in `tar'.
`archive'
`-a' in `cp'.
`archive-name'
`-n' in `shar'.
`arglength'
`-l' in `m4'.
`ascii'
`-a' in `diff'.
`assign'
`-v' in `gawk'.
`assume-new'
`-W' in `make'.
`assume-old'
`-o' in `make'.
`auto-check'
`-a' in `recode'.
`auto-pager'
`-a' in `wdiff'.
`auto-reference'
`-A' in `ptx'.
`avoid-wraps'
`-n' in `wdiff'.
`background'
For server programs, run in the background.
`backward-search'
`-B' in `ctags'.
`basename'
`-f' in `shar'.
`batch'
Used in GDB.
`baud'
Used in GDB.
`before'
`-b' in `tac'.
`binary'
`-b' in `cpio' and `diff'.
`bits-per-code'
`-b' in `shar'.
`block-size'
Used in `cpio' and `tar'.
`blocks'
`-b' in `head' and `tail'.
`break-file'
`-b' in `ptx'.
`brief'
Used in various programs to make output shorter.
`bytes'
`-c' in `head', `split', and `tail'.
`c++'
`-C' in `etags'.
`catenate'
`-A' in `tar'.
`cd'
Used in various programs to specify the directory to use.
`changes'
`-c' in `chgrp' and `chown'.
`classify'
`-F' in `ls'.
`colons'
`-c' in `recode'.
`command'
`-c' in `su'; `-x' in GDB.
`compare'
`-d' in `tar'.
`compat'
Used in `gawk'.
`compress'
`-Z' in `tar' and `shar'.
`concatenate'
`-A' in `tar'.
`confirmation'
`-w' in `tar'.
`context'
Used in `diff'.
`copyleft'
`-W copyleft' in `gawk'.
`copyright'
`-C' in `ptx', `recode', and `wdiff'; `-W copyright' in `gawk'.
`core'
Used in GDB.
`count'
`-q' in `who'.
`count-links'
`-l' in `du'.
`create'
Used in `tar' and `cpio'.
`cut-mark'
`-c' in `shar'.
`cxref'
`-x' in `ctags'.
`date'
`-d' in `touch'.
`debug'
`-d' in `make' and `m4'; `-t' in Bison.
`define'
`-D' in `m4'.
`defines'
`-d' in Bison and `ctags'.
`delete'
`-D' in `tar'.
`dereference'
`-L' in `chgrp', `chown', `cpio', `du', `ls', and `tar'.
`dereference-args'
`-D' in `du'.
`device'
Specify an I/O device (special file name).
`diacritics'
`-d' in `recode'.
`dictionary-order'
`-d' in `look'.
`diff'
`-d' in `tar'.
`digits'
`-n' in `csplit'.
`directory'
Specify the directory to use, in various programs. In `ls', it
means to show directories themselves rather than their contents.
In `rm' and `ln', it means to not treat links to directories
specially.
`discard-all'
`-x' in `strip'.
`discard-locals'
`-X' in `strip'.
`dry-run'
`-n' in `make'.
`ed'
`-e' in `diff'.
`elide-empty-files'
`-z' in `csplit'.
`end-delete'
`-x' in `wdiff'.
`end-insert'
`-z' in `wdiff'.
`entire-new-file'
`-N' in `diff'.
`environment-overrides'
`-e' in `make'.
`eof'
`-e' in `xargs'.
`epoch'
Used in GDB.
`error-limit'
Used in `makeinfo'.
`error-output'
`-o' in `m4'.
`escape'
`-b' in `ls'.
`exclude-from'
`-X' in `tar'.
`exec'
Used in GDB.
`exit'
`-x' in `xargs'.
`exit-0'
`-e' in `unshar'.
`expand-tabs'
`-t' in `diff'.
`expression'
`-e' in `sed'.
`extern-only'
`-g' in `nm'.
`extract'
`-i' in `cpio'; `-x' in `tar'.
`faces'
`-f' in `finger'.
`fast'
`-f' in `su'.
`fatal-warnings'
`-E' in `m4'.
`file'
`-f' in `gawk', `info', `make', `mt', `sed', and `tar'.
`field-separator'
`-F' in `gawk'.
`file-prefix'
`-b' in Bison.
`file-type'
`-F' in `ls'.
`files-from'
`-T' in `tar'.
`fill-column'
Used in `makeinfo'.
`flag-truncation'
`-F' in `ptx'.
`fixed-output-files'
`-y' in Bison.
`follow'
`-f' in `tail'.
`footnote-style'
Used in `makeinfo'.
`force'
`-f' in `cp', `ln', `mv', and `rm'.
`force-prefix'
`-F' in `shar'.
`foreground'
For server programs, run in the foreground; in other words, don't
do anything special to run the server in the background.
`format'
Used in `ls', `time', and `ptx'.
`freeze-state'
`-F' in `m4'.
`fullname'
Used in GDB.
`gap-size'
`-g' in `ptx'.
`get'
`-x' in `tar'.
`graphic'
`-i' in `ul'.
`graphics'
`-g' in `recode'.
`group'
`-g' in `install'.
`gzip'
`-z' in `tar' and `shar'.
`hashsize'
`-H' in `m4'.
`header'
`-h' in `objdump' and `recode'
`heading'
`-H' in `who'.
`help'
Used to ask for brief usage information.
`here-delimiter'
`-d' in `shar'.
`hide-control-chars'
`-q' in `ls'.
`html'
In `makeinfo', output HTML.
`idle'
`-u' in `who'.
`ifdef'
`-D' in `diff'.
`ignore'
`-I' in `ls'; `-x' in `recode'.
`ignore-all-space'
`-w' in `diff'.
`ignore-backups'
`-B' in `ls'.
`ignore-blank-lines'
`-B' in `diff'.
`ignore-case'
`-f' in `look' and `ptx'; `-i' in `diff' and `wdiff'.
`ignore-errors'
`-i' in `make'.
`ignore-file'
`-i' in `ptx'.
`ignore-indentation'
`-I' in `etags'.
`ignore-init-file'
`-f' in Oleo.
`ignore-interrupts'
`-i' in `tee'.
`ignore-matching-lines'
`-I' in `diff'.
`ignore-space-change'
`-b' in `diff'.
`ignore-zeros'
`-i' in `tar'.
`include'
`-i' in `etags'; `-I' in `m4'.
`include-dir'
`-I' in `make'.
`incremental'
`-G' in `tar'.
`info'
`-i', `-l', and `-m' in Finger.
`init-file'
In some programs, specify the name of the file to read as the
user's init file.
`initial'
`-i' in `expand'.
`initial-tab'
`-T' in `diff'.
`inode'
`-i' in `ls'.
`interactive'
`-i' in `cp', `ln', `mv', `rm'; `-e' in `m4'; `-p' in `xargs';
`-w' in `tar'.
`intermix-type'
`-p' in `shar'.
`iso-8601'
Used in `date'
`jobs'
`-j' in `make'.
`just-print'
`-n' in `make'.
`keep-going'
`-k' in `make'.
`keep-files'
`-k' in `csplit'.
`kilobytes'
`-k' in `du' and `ls'.
`language'
`-l' in `etags'.
`less-mode'
`-l' in `wdiff'.
`level-for-gzip'
`-g' in `shar'.
`line-bytes'
`-C' in `split'.
`lines'
Used in `split', `head', and `tail'.
`link'
`-l' in `cpio'.
`lint'
`lint-old'
Used in `gawk'.
`list'
`-t' in `cpio'; `-l' in `recode'.
`list'
`-t' in `tar'.
`literal'
`-N' in `ls'.
`load-average'
`-l' in `make'.
`login'
Used in `su'.
`machine'
Used in `uname'.
`macro-name'
`-M' in `ptx'.
`mail'
`-m' in `hello' and `uname'.
`make-directories'
`-d' in `cpio'.
`makefile'
`-f' in `make'.
`mapped'
Used in GDB.
`max-args'
`-n' in `xargs'.
`max-chars'
`-n' in `xargs'.
`max-lines'
`-l' in `xargs'.
`max-load'
`-l' in `make'.
`max-procs'
`-P' in `xargs'.
`mesg'
`-T' in `who'.
`message'
`-T' in `who'.
`minimal'
`-d' in `diff'.
`mixed-uuencode'
`-M' in `shar'.
`mode'
`-m' in `install', `mkdir', and `mkfifo'.
`modification-time'
`-m' in `tar'.
`multi-volume'
`-M' in `tar'.
`name-prefix'
`-a' in Bison.
`nesting-limit'
`-L' in `m4'.
`net-headers'
`-a' in `shar'.
`new-file'
`-W' in `make'.
`no-builtin-rules'
`-r' in `make'.
`no-character-count'
`-w' in `shar'.
`no-check-existing'
`-x' in `shar'.
`no-common'
`-3' in `wdiff'.
`no-create'
`-c' in `touch'.
`no-defines'
`-D' in `etags'.
`no-deleted'
`-1' in `wdiff'.
`no-dereference'
`-d' in `cp'.
`no-inserted'
`-2' in `wdiff'.
`no-keep-going'
`-S' in `make'.
`no-lines'
`-l' in Bison.
`no-piping'
`-P' in `shar'.
`no-prof'
`-e' in `gprof'.
`no-regex'
`-R' in `etags'.
`no-sort'
`-p' in `nm'.
`no-splash'
Don't print a startup splash screen.
`no-split'
Used in `makeinfo'.
`no-static'
`-a' in `gprof'.
`no-time'
`-E' in `gprof'.
`no-timestamp'
`-m' in `shar'.
`no-validate'
Used in `makeinfo'.
`no-wait'
Used in `emacsclient'.
`no-warn'
Used in various programs to inhibit warnings.
`node'
`-n' in `info'.
`nodename'
`-n' in `uname'.
`nonmatching'
`-f' in `cpio'.
`nstuff'
`-n' in `objdump'.
`null'
`-0' in `xargs'.
`number'
`-n' in `cat'.
`number-nonblank'
`-b' in `cat'.
`numeric-sort'
`-n' in `nm'.
`numeric-uid-gid'
`-n' in `cpio' and `ls'.
`nx'
Used in GDB.
`old-archive'
`-o' in `tar'.
`old-file'
`-o' in `make'.
`one-file-system'
`-l' in `tar', `cp', and `du'.
`only-file'
`-o' in `ptx'.
`only-prof'
`-f' in `gprof'.
`only-time'
`-F' in `gprof'.
`options'
`-o' in `getopt', `fdlist', `fdmount', `fdmountd', and `fdumount'.
`output'
In various programs, specify the output file name.
`output-prefix'
`-o' in `shar'.
`override'
`-o' in `rm'.
`overwrite'
`-c' in `unshar'.
`owner'
`-o' in `install'.
`paginate'
`-l' in `diff'.
`paragraph-indent'
Used in `makeinfo'.
`parents'
`-p' in `mkdir' and `rmdir'.
`pass-all'
`-p' in `ul'.
`pass-through'
`-p' in `cpio'.
`port'
`-P' in `finger'.
`portability'
`-c' in `cpio' and `tar'.
`posix'
Used in `gawk'.
`prefix-builtins'
`-P' in `m4'.
`prefix'
`-f' in `csplit'.
`preserve'
Used in `tar' and `cp'.
`preserve-environment'
`-p' in `su'.
`preserve-modification-time'
`-m' in `cpio'.
`preserve-order'
`-s' in `tar'.
`preserve-permissions'
`-p' in `tar'.
`print'
`-l' in `diff'.
`print-chars'
`-L' in `cmp'.
`print-data-base'
`-p' in `make'.
`print-directory'
`-w' in `make'.
`print-file-name'
`-o' in `nm'.
`print-symdefs'
`-s' in `nm'.
`printer'
`-p' in `wdiff'.
`prompt'
`-p' in `ed'.
`proxy'
Specify an HTTP proxy.
`query-user'
`-X' in `shar'.
`question'
`-q' in `make'.
`quiet'
Used in many programs to inhibit the usual output. Every program
accepting `--quiet' should accept `--silent' as a synonym.
`quiet-unshar'
`-Q' in `shar'
`quote-name'
`-Q' in `ls'.
`rcs'
`-n' in `diff'.
`re-interval'
Used in `gawk'.
`read-full-blocks'
`-B' in `tar'.
`readnow'
Used in GDB.
`recon'
`-n' in `make'.
`record-number'
`-R' in `tar'.
`recursive'
Used in `chgrp', `chown', `cp', `ls', `diff', and `rm'.
`reference'
`-r' in `touch'.
`references'
`-r' in `ptx'.
`regex'
`-r' in `tac' and `etags'.
`release'
`-r' in `uname'.
`reload-state'
`-R' in `m4'.
`relocation'
`-r' in `objdump'.
`rename'
`-r' in `cpio'.
`replace'
`-i' in `xargs'.
`report-identical-files'
`-s' in `diff'.
`reset-access-time'
`-a' in `cpio'.
`reverse'
`-r' in `ls' and `nm'.
`reversed-ed'
`-f' in `diff'.
`right-side-defs'
`-R' in `ptx'.
`same-order'
`-s' in `tar'.
`same-permissions'
`-p' in `tar'.
`save'
`-g' in `stty'.
`se'
Used in GDB.
`sentence-regexp'
`-S' in `ptx'.
`separate-dirs'
`-S' in `du'.
`separator'
`-s' in `tac'.
`sequence'
Used by `recode' to chose files or pipes for sequencing passes.
`shell'
`-s' in `su'.
`show-all'
`-A' in `cat'.
`show-c-function'
`-p' in `diff'.
`show-ends'
`-E' in `cat'.
`show-function-line'
`-F' in `diff'.
`show-tabs'
`-T' in `cat'.
`silent'
Used in many programs to inhibit the usual output. Every program
accepting `--silent' should accept `--quiet' as a synonym.
`size'
`-s' in `ls'.
`socket'
Specify a file descriptor for a network server to use for its
socket, instead of opening and binding a new socket. This
provides a way to run, in a non-privileged process, a server that
normally needs a reserved port number.
`sort'
Used in `ls'.
`source'
`-W source' in `gawk'.
`sparse'
`-S' in `tar'.
`speed-large-files'
`-H' in `diff'.
`split-at'
`-E' in `unshar'.
`split-size-limit'
`-L' in `shar'.
`squeeze-blank'
`-s' in `cat'.
`start-delete'
`-w' in `wdiff'.
`start-insert'
`-y' in `wdiff'.
`starting-file'
Used in `tar' and `diff' to specify which file within a directory
to start processing with.
`statistics'
`-s' in `wdiff'.
`stdin-file-list'
`-S' in `shar'.
`stop'
`-S' in `make'.
`strict'
`-s' in `recode'.
`strip'
`-s' in `install'.
`strip-all'
`-s' in `strip'.
`strip-debug'
`-S' in `strip'.
`submitter'
`-s' in `shar'.
`suffix'
`-S' in `cp', `ln', `mv'.
`suffix-format'
`-b' in `csplit'.
`sum'
`-s' in `gprof'.
`summarize'
`-s' in `du'.
`symbolic'
`-s' in `ln'.
`symbols'
Used in GDB and `objdump'.
`synclines'
`-s' in `m4'.
`sysname'
`-s' in `uname'.
`tabs'
`-t' in `expand' and `unexpand'.
`tabsize'
`-T' in `ls'.
`terminal'
`-T' in `tput' and `ul'. `-t' in `wdiff'.
`text'
`-a' in `diff'.
`text-files'
`-T' in `shar'.
`time'
Used in `ls' and `touch'.
`timeout'
Specify how long to wait before giving up on some operation.
`to-stdout'
`-O' in `tar'.
`total'
`-c' in `du'.
`touch'
`-t' in `make', `ranlib', and `recode'.
`trace'
`-t' in `m4'.
`traditional'
`-t' in `hello'; `-W traditional' in `gawk'; `-G' in `ed', `m4',
and `ptx'.
`tty'
Used in GDB.
`typedefs'
`-t' in `ctags'.
`typedefs-and-c++'
`-T' in `ctags'.
`typeset-mode'
`-t' in `ptx'.
`uncompress'
`-z' in `tar'.
`unconditional'
`-u' in `cpio'.
`undefine'
`-U' in `m4'.
`undefined-only'
`-u' in `nm'.
`update'
`-u' in `cp', `ctags', `mv', `tar'.
`usage'
Used in `gawk'; same as `--help'.
`uuencode'
`-B' in `shar'.
`vanilla-operation'
`-V' in `shar'.
`verbose'
Print more information about progress. Many programs support this.
`verify'
`-W' in `tar'.
`version'
Print the version number.
`version-control'
`-V' in `cp', `ln', `mv'.
`vgrind'
`-v' in `ctags'.
`volume'
`-V' in `tar'.
`what-if'
`-W' in `make'.
`whole-size-limit'
`-l' in `shar'.
`width'
`-w' in `ls' and `ptx'.
`word-regexp'
`-W' in `ptx'.
`writable'
`-T' in `who'.
`zeros'
`-z' in `gprof'.
File: standards.info, Node: OID Allocations, Next: Memory Usage, Prev: Option Table, Up: Program Behavior
4.10 OID Allocations
====================
The OID (object identifier) 1.3.6.1.4.1.11591 has been assigned to the
GNU Project (thanks to Werner Koch). These are used for SNMP, LDAP,
X.509 certificates, and so on. The web site
`http://www.alvestrand.no/objectid' has a (voluntary) listing of many
OID assignments.
If you need a new slot for your GNU package, write
. Here is a list of arcs currently assigned:
1.3.6.1.4.1.11591 GNU
1.3.6.1.4.1.11591.1 GNU Radius
1.3.6.1.4.1.11591.2 GnuPG
1.3.6.1.4.1.11591.2.1 notation
1.3.6.1.4.1.11591.2.1.1 pkaAddress
1.3.6.1.4.1.11591.3 GNU Radar
1.3.6.1.4.1.11591.4 GNU GSS
1.3.6.1.4.1.11591.5 GNU Mailutils
1.3.6.1.4.1.11591.6 GNU Shishi
1.3.6.1.4.1.11591.7 GNU Radio
1.3.6.1.4.1.11591.8 GNU Dico
1.3.6.1.4.1.11591.12 digestAlgorithm
1.3.6.1.4.1.11591.12.2 TIGER/192
1.3.6.1.4.1.11591.13 encryptionAlgorithm
1.3.6.1.4.1.11591.13.2 Serpent
1.3.6.1.4.1.11591.13.2.1 Serpent-128-ECB
1.3.6.1.4.1.11591.13.2.2 Serpent-128-CBC
1.3.6.1.4.1.11591.13.2.3 Serpent-128-OFB
1.3.6.1.4.1.11591.13.2.4 Serpent-128-CFB
1.3.6.1.4.1.11591.13.2.21 Serpent-192-ECB
1.3.6.1.4.1.11591.13.2.22 Serpent-192-CBC
1.3.6.1.4.1.11591.13.2.23 Serpent-192-OFB
1.3.6.1.4.1.11591.13.2.24 Serpent-192-CFB
1.3.6.1.4.1.11591.13.2.41 Serpent-256-ECB
1.3.6.1.4.1.11591.13.2.42 Serpent-256-CBC
1.3.6.1.4.1.11591.13.2.43 Serpent-256-OFB
1.3.6.1.4.1.11591.13.2.44 Serpent-256-CFB
1.3.6.1.4.1.11591.14 CRC algorithms
1.3.6.1.4.1.11591.14.1 CRC 32
File: standards.info, Node: Memory Usage, Next: File Usage, Prev: OID Allocations, Up: Program Behavior
4.11 Memory Usage
=================
If a program typically uses just a few meg of memory, don't bother
making any effort to reduce memory usage. For example, if it is
impractical for other reasons to operate on files more than a few meg
long, it is reasonable to read entire input files into memory to
operate on them.
However, for programs such as `cat' or `tail', that can usefully
operate on very large files, it is important to avoid using a technique
that would artificially limit the size of files it can handle. If a
program works by lines and could be applied to arbitrary user-supplied
input files, it should keep only a line in memory, because this is not
very hard and users will want to be able to operate on input files that
are bigger than will fit in memory all at once.
If your program creates complicated data structures, just make them
in memory and give a fatal error if `malloc' returns zero.
Memory analysis tools such as `valgrind' can be useful, but don't
complicate a program merely to avoid their false alarms. For example,
if memory is used until just before a process exits, don't free it
simply to silence such a tool.
File: standards.info, Node: File Usage, Prev: Memory Usage, Up: Program Behavior
4.12 File Usage
===============
Programs should be prepared to operate when `/usr' and `/etc' are
read-only file systems. Thus, if the program manages log files, lock
files, backup files, score files, or any other files which are modified
for internal purposes, these files should not be stored in `/usr' or
`/etc'.
There are two exceptions. `/etc' is used to store system
configuration information; it is reasonable for a program to modify
files in `/etc' when its job is to update the system configuration.
Also, if the user explicitly asks to modify one file in a directory, it
is reasonable for the program to store other files in the same
directory.
File: standards.info, Node: Writing C, Next: Documentation, Prev: Program Behavior, Up: Top
5 Making The Best Use of C
**************************
This chapter provides advice on how best to use the C language when
writing GNU software.
* Menu:
* Formatting:: Formatting your source code.
* Comments:: Commenting your work.
* Syntactic Conventions:: Clean use of C constructs.
* Names:: Naming variables, functions, and files.
* System Portability:: Portability among different operating systems.
* CPU Portability:: Supporting the range of CPU types.
* System Functions:: Portability and ``standard'' library functions.
* Internationalization:: Techniques for internationalization.
* Character Set:: Use ASCII by default.
* Quote Characters:: Use "..." or '...' in the C locale.
* Mmap:: How you can safely use `mmap'.
File: standards.info, Node: Formatting, Next: Comments, Up: Writing C
5.1 Formatting Your Source Code
===============================
It is important to put the open-brace that starts the body of a C
function in column one, so that they will start a defun. Several tools
look for open-braces in column one to find the beginnings of C
functions. These tools will not work on code not formatted that way.
Avoid putting open-brace, open-parenthesis or open-bracket in column
one when they are inside a function, so that they won't start a defun.
The open-brace that starts a `struct' body can go in column one if you
find it useful to treat that definition as a defun.
It is also important for function definitions to start the name of
the function in column one. This helps people to search for function
definitions, and may also help certain tools recognize them. Thus,
using Standard C syntax, the format is this:
static char *
concat (char *s1, char *s2)
{
...
}
or, if you want to use traditional C syntax, format the definition like
this:
static char *
concat (s1, s2) /* Name starts in column one here */
char *s1, *s2;
{ /* Open brace in column one here */
...
}
In Standard C, if the arguments don't fit nicely on one line, split
it like this:
int
lots_of_args (int an_integer, long a_long, short a_short,
double a_double, float a_float)
...
For `struct' and `enum' types, likewise put the braces in column
one, unless the whole contents fits on one line:
struct foo
{
int a, b;
}
or
struct foo { int a, b; }
The rest of this section gives our recommendations for other aspects
of C formatting style, which is also the default style of the `indent'
program in version 1.2 and newer. It corresponds to the options
-nbad -bap -nbc -bbo -bl -bli2 -bls -ncdb -nce -cp1 -cs -di2
-ndj -nfc1 -nfca -hnl -i2 -ip5 -lp -pcs -psl -nsc -nsob
We don't think of these recommendations as requirements, because it
causes no problems for users if two different programs have different
formatting styles.
But whatever style you use, please use it consistently, since a
mixture of styles within one program tends to look ugly. If you are
contributing changes to an existing program, please follow the style of
that program.
For the body of the function, our recommended style looks like this:
if (x < foo (y, z))
haha = bar[4] + 5;
else
{
while (z)
{
haha += foo (z, z);
z--;
}
return ++x + bar ();
}
We find it easier to read a program when it has spaces before the
open-parentheses and after the commas. Especially after the commas.
When you split an expression into multiple lines, split it before an
operator, not after one. Here is the right way:
if (foo_this_is_long && bar > win (x, y, z)
&& remaining_condition)
Try to avoid having two operators of different precedence at the same
level of indentation. For example, don't write this:
mode = (inmode[j] == VOIDmode
|| GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j])
? outmode[j] : inmode[j]);
Instead, use extra parentheses so that the indentation shows the
nesting:
mode = ((inmode[j] == VOIDmode
|| (GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j])))
? outmode[j] : inmode[j]);
Insert extra parentheses so that Emacs will indent the code properly.
For example, the following indentation looks nice if you do it by hand,
v = rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000
+ rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000;
but Emacs would alter it. Adding a set of parentheses produces
something that looks equally nice, and which Emacs will preserve:
v = (rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000
+ rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000);
Format do-while statements like this:
do
{
a = foo (a);
}
while (a > 0);
Please use formfeed characters (control-L) to divide the program into
pages at logical places (but not within a function). It does not matter
just how long the pages are, since they do not have to fit on a printed
page. The formfeeds should appear alone on lines by themselves.
File: standards.info, Node: Comments, Next: Syntactic Conventions, Prev: Formatting, Up: Writing C
5.2 Commenting Your Work
========================
Every program should start with a comment saying briefly what it is for.
Example: `fmt - filter for simple filling of text'. This comment
should be at the top of the source file containing the `main' function
of the program.
Also, please write a brief comment at the start of each source file,
with the file name and a line or two about the overall purpose of the
file.
Please write the comments in a GNU program in English, because
English is the one language that nearly all programmers in all
countries can read. If you do not write English well, please write
comments in English as well as you can, then ask other people to help
rewrite them. If you can't write comments in English, please find
someone to work with you and translate your comments into English.
Please put a comment on each function saying what the function does,
what sorts of arguments it gets, and what the possible values of
arguments mean and are used for. It is not necessary to duplicate in
words the meaning of the C argument declarations, if a C type is being
used in its customary fashion. If there is anything nonstandard about
its use (such as an argument of type `char *' which is really the
address of the second character of a string, not the first), or any
possible values that would not work the way one would expect (such as,
that strings containing newlines are not guaranteed to work), be sure
to say so.
Also explain the significance of the return value, if there is one.
Please put two spaces after the end of a sentence in your comments,
so that the Emacs sentence commands will work. Also, please write
complete sentences and capitalize the first word. If a lower-case
identifier comes at the beginning of a sentence, don't capitalize it!
Changing the spelling makes it a different identifier. If you don't
like starting a sentence with a lower case letter, write the sentence
differently (e.g., "The identifier lower-case is ...").
The comment on a function is much clearer if you use the argument
names to speak about the argument values. The variable name itself
should be lower case, but write it in upper case when you are speaking
about the value rather than the variable itself. Thus, "the inode
number NODE_NUM" rather than "an inode".
There is usually no purpose in restating the name of the function in
the comment before it, because readers can see that for themselves.
There might be an exception when the comment is so long that the
function itself would be off the bottom of the screen.
There should be a comment on each static variable as well, like this:
/* Nonzero means truncate lines in the display;
zero means continue them. */
int truncate_lines;
Every `#endif' should have a comment, except in the case of short
conditionals (just a few lines) that are not nested. The comment should
state the condition of the conditional that is ending, _including its
sense_. `#else' should have a comment describing the condition _and
sense_ of the code that follows. For example:
#ifdef foo
...
#else /* not foo */
...
#endif /* not foo */
#ifdef foo
...
#endif /* foo */
but, by contrast, write the comments this way for a `#ifndef':
#ifndef foo
...
#else /* foo */
...
#endif /* foo */
#ifndef foo
...
#endif /* not foo */
File: standards.info, Node: Syntactic Conventions, Next: Names, Prev: Comments, Up: Writing C
5.3 Clean Use of C Constructs
=============================
Please explicitly declare the types of all objects. For example, you
should explicitly declare all arguments to functions, and you should
declare functions to return `int' rather than omitting the `int'.
Some programmers like to use the GCC `-Wall' option, and change the
code whenever it issues a warning. If you want to do this, then do.
Other programmers prefer not to use `-Wall', because it gives warnings
for valid and legitimate code which they do not want to change. If you
want to do this, then do. The compiler should be your servant, not
your master.
Don't make the program ugly just to placate static analysis tools
such as `lint', `clang', and GCC with extra warnings options such as
`-Wconversion' and `-Wundef'. These tools can help find bugs and
unclear code, but they can also generate so many false alarms that it
hurts readability to silence them with unnecessary casts, wrappers, and
other complications. For example, please don't insert casts to `void'
or calls to do-nothing functions merely to pacify a lint checker.
Declarations of external functions and functions to appear later in
the source file should all go in one place near the beginning of the
file (somewhere before the first function definition in the file), or
else should go in a header file. Don't put `extern' declarations inside
functions.
It used to be common practice to use the same local variables (with
names like `tem') over and over for different values within one
function. Instead of doing this, it is better to declare a separate
local variable for each distinct purpose, and give it a name which is
meaningful. This not only makes programs easier to understand, it also
facilitates optimization by good compilers. You can also move the
declaration of each local variable into the smallest scope that includes
all its uses. This makes the program even cleaner.
Don't use local variables or parameters that shadow global
identifiers. GCC's `-Wshadow' option can detect this problem.
Don't declare multiple variables in one declaration that spans lines.
Start a new declaration on each line, instead. For example, instead of
this:
int foo,
bar;
write either this:
int foo, bar;
or this:
int foo;
int bar;
(If they are global variables, each should have a comment preceding it
anyway.)
When you have an `if'-`else' statement nested in another `if'
statement, always put braces around the `if'-`else'. Thus, never write
like this:
if (foo)
if (bar)
win ();
else
lose ();
always like this:
if (foo)
{
if (bar)
win ();
else
lose ();
}
If you have an `if' statement nested inside of an `else' statement,
either write `else if' on one line, like this,
if (foo)
...
else if (bar)
...
with its `then'-part indented like the preceding `then'-part, or write
the nested `if' within braces like this:
if (foo)
...
else
{
if (bar)
...
}
Don't declare both a structure tag and variables or typedefs in the
same declaration. Instead, declare the structure tag separately and
then use it to declare the variables or typedefs.
Try to avoid assignments inside `if'-conditions (assignments inside
`while'-conditions are ok). For example, don't write this:
if ((foo = (char *) malloc (sizeof *foo)) == 0)
fatal ("virtual memory exhausted");
instead, write this:
foo = (char *) malloc (sizeof *foo);
if (foo == 0)
fatal ("virtual memory exhausted");
This example uses zero without a cast as a null pointer constant.
This is perfectly fine, except that a cast is needed when calling a
varargs function or when using `sizeof'.
File: standards.info, Node: Names, Next: System Portability, Prev: Syntactic Conventions, Up: Writing C
5.4 Naming Variables, Functions, and Files
==========================================
The names of global variables and functions in a program serve as
comments of a sort. So don't choose terse names--instead, look for
names that give useful information about the meaning of the variable or
function. In a GNU program, names should be English, like other
comments.
Local variable names can be shorter, because they are used only
within one context, where (presumably) comments explain their purpose.
Try to limit your use of abbreviations in symbol names. It is ok to
make a few abbreviations, explain what they mean, and then use them
frequently, but don't use lots of obscure abbreviations.
Please use underscores to separate words in a name, so that the Emacs
word commands can be useful within them. Stick to lower case; reserve
upper case for macros and `enum' constants, and for name-prefixes that
follow a uniform convention.
For example, you should use names like `ignore_space_change_flag';
don't use names like `iCantReadThis'.
Variables that indicate whether command-line options have been
specified should be named after the meaning of the option, not after
the option-letter. A comment should state both the exact meaning of
the option and its letter. For example,
/* Ignore changes in horizontal whitespace (-b). */
int ignore_space_change_flag;
When you want to define names with constant integer values, use
`enum' rather than `#define'. GDB knows about enumeration constants.
You might want to make sure that none of the file names would
conflict if the files were loaded onto an MS-DOS file system which
shortens the names. You can use the program `doschk' to test for this.
Some GNU programs were designed to limit themselves to file names of
14 characters or less, to avoid file name conflicts if they are read
into older System V systems. Please preserve this feature in the
existing GNU programs that have it, but there is no need to do this in
new GNU programs. `doschk' also reports file names longer than 14
characters.
File: standards.info, Node: System Portability, Next: CPU Portability, Prev: Names, Up: Writing C
5.5 Portability between System Types
====================================
In the Unix world, "portability" refers to porting to different Unix
versions. For a GNU program, this kind of portability is desirable, but
not paramount.
The primary purpose of GNU software is to run on top of the GNU
kernel, compiled with the GNU C compiler, on various types of CPU. So
the kinds of portability that are absolutely necessary are quite
limited. But it is important to support Linux-based GNU systems, since
they are the form of GNU that is popular.
Beyond that, it is good to support the other free operating systems
(*BSD), and it is nice to support other Unix-like systems if you want
to. Supporting a variety of Unix-like systems is desirable, although
not paramount. It is usually not too hard, so you may as well do it.
But you don't have to consider it an obligation, if it does turn out to
be hard.
The easiest way to achieve portability to most Unix-like systems is
to use Autoconf. It's unlikely that your program needs to know more
information about the host platform than Autoconf can provide, simply
because most of the programs that need such knowledge have already been
written.
Avoid using the format of semi-internal data bases (e.g.,
directories) when there is a higher-level alternative (`readdir').
As for systems that are not like Unix, such as MSDOS, Windows, VMS,
MVS, and older Macintosh systems, supporting them is often a lot of
work. When that is the case, it is better to spend your time adding
features that will be useful on GNU and GNU/Linux, rather than on
supporting other incompatible systems.
If you do support Windows, please do not abbreviate it as "win". In
hacker terminology, calling something a "win" is a form of praise.
You're free to praise Microsoft Windows on your own if you want, but
please don't do this in GNU packages. Instead of abbreviating
"Windows" to "win", you can write it in full or abbreviate it to "woe"
or "w". In GNU Emacs, for instance, we use `w32' in file names of
Windows-specific files, but the macro for Windows conditionals is
called `WINDOWSNT'.
It is a good idea to define the "feature test macro" `_GNU_SOURCE'
when compiling your C files. When you compile on GNU or GNU/Linux,
this will enable the declarations of GNU library extension functions,
and that will usually give you a compiler error message if you define
the same function names in some other way in your program. (You don't
have to actually _use_ these functions, if you prefer to make the
program more portable to other systems.)
But whether or not you use these GNU extensions, you should avoid
using their names for any other meanings. Doing so would make it hard
to move your code into other GNU programs.
File: standards.info, Node: CPU Portability, Next: System Functions, Prev: System Portability, Up: Writing C
5.6 Portability between CPUs
============================
Even GNU systems will differ because of differences among CPU
types--for example, difference in byte ordering and alignment
requirements. It is absolutely essential to handle these differences.
However, don't make any effort to cater to the possibility that an
`int' will be less than 32 bits. We don't support 16-bit machines in
GNU.
Similarly, don't make any effort to cater to the possibility that
`long' will be smaller than predefined types like `size_t'. For
example, the following code is ok:
printf ("size = %lu\n", (unsigned long) sizeof array);
printf ("diff = %ld\n", (long) (pointer2 - pointer1));
1989 Standard C requires this to work, and we know of only one
counterexample: 64-bit programs on Microsoft Windows. We will leave it
to those who want to port GNU programs to that environment to figure
out how to do it.
Predefined file-size types like `off_t' are an exception: they are
longer than `long' on many platforms, so code like the above won't work
with them. One way to print an `off_t' value portably is to print its
digits yourself, one by one.
Don't assume that the address of an `int' object is also the address
of its least-significant byte. This is false on big-endian machines.
Thus, don't make the following mistake:
int c;
...
while ((c = getchar ()) != EOF)
write (file_descriptor, &c, 1);
Instead, use `unsigned char' as follows. (The `unsigned' is for
portability to unusual systems where `char' is signed and where there
is integer overflow checking.)
int c;
while ((c = getchar ()) != EOF)
{
unsigned char u = c;
write (file_descriptor, &u, 1);
}
Avoid casting pointers to integers if you can. Such casts greatly
reduce portability, and in most programs they are easy to avoid. In the
cases where casting pointers to integers is essential--such as, a Lisp
interpreter which stores type information as well as an address in one
word--you'll have to make explicit provisions to handle different word
sizes. You will also need to make provision for systems in which the
normal range of addresses you can get from `malloc' starts far away
from zero.
File: standards.info, Node: System Functions, Next: Internationalization, Prev: CPU Portability, Up: Writing C
5.7 Calling System Functions
============================
Historically, C implementations differed substantially, and many
systems lacked a full implementation of ANSI/ISO C89. Nowadays,
however, very few systems lack a C89 compiler and GNU C supports almost
all of C99. Similarly, most systems implement POSIX.1-1993 libraries
and tools, and many have POSIX.1-2001.
Hence, there is little reason to support old C or non-POSIX systems,
and you may want to take advantage of C99 and POSIX-1.2001 to write
clearer, more portable, or faster code. You should use standard
interfaces where possible; but if GNU extensions make your program more
maintainable, powerful, or otherwise better, don't hesitate to use
them. In any case, don't make your own declaration of system
functions; that's a recipe for conflict.
Despite the standards, nearly every library function has some sort of
portability issue on some system or another. Here are some examples:
`open'
Names with trailing `/''s are mishandled on many platforms.
`printf'
`long double' may be unimplemented; floating values Infinity and
NaN are often mishandled; output for large precisions may be
incorrect.
`readlink'
May return `int' instead of `ssize_t'.
`scanf'
On Windows, `errno' is not set on failure.
Gnulib (http://www.gnu.org/software/gnulib/) is a big help in this
regard. Gnulib provides implementations of standard interfaces on many
of the systems that lack them, including portable implementations of
enhanced GNU interfaces, thereby making their use portable, and of
POSIX-1.2008 interfaces, some of which are missing even on up-to-date
GNU systems.
Gnulib also provides many useful non-standard interfaces; for
example, C implementations of standard data structures (hash tables,
binary trees), error-checking type-safe wrappers for memory allocation
functions (`xmalloc', `xrealloc'), and output of error messages.
Gnulib integrates with GNU Autoconf and Automake to remove much of
the burden of writing portable code from the programmer: Gnulib makes
your configure script automatically determine what features are missing
and use the Gnulib code to supply the missing pieces.
The Gnulib and Autoconf manuals have extensive sections on
portability: *note Introduction: (gnulib)Top. and *note Portable C and
C++: (autoconf)Portable C and C++. Please consult them for many more
details.
File: standards.info, Node: Internationalization, Next: Character Set, Prev: System Functions, Up: Writing C
5.8 Internationalization
========================
GNU has a library called GNU gettext that makes it easy to translate the
messages in a program into various languages. You should use this
library in every program. Use English for the messages as they appear
in the program, and let gettext provide the way to translate them into
other languages.
Using GNU gettext involves putting a call to the `gettext' macro
around each string that might need translation--like this:
printf (gettext ("Processing file '%s'..."), file);
This permits GNU gettext to replace the string `"Processing file
'%s'..."' with a translated version.
Once a program uses gettext, please make a point of writing calls to
`gettext' when you add new strings that call for translation.
Using GNU gettext in a package involves specifying a "text domain
name" for the package. The text domain name is used to separate the
translations for this package from the translations for other packages.
Normally, the text domain name should be the same as the name of the
package--for example, `coreutils' for the GNU core utilities.
To enable gettext to work well, avoid writing code that makes
assumptions about the structure of words or sentences. When you want
the precise text of a sentence to vary depending on the data, use two or
more alternative string constants each containing a complete sentences,
rather than inserting conditionalized words or phrases into a single
sentence framework.
Here is an example of what not to do:
printf ("%s is full", capacity > 5000000 ? "disk" : "floppy disk");
If you apply gettext to all strings, like this,
printf (gettext ("%s is full"),
capacity > 5000000 ? gettext ("disk") : gettext ("floppy disk"));
the translator will hardly know that "disk" and "floppy disk" are meant
to be substituted in the other string. Worse, in some languages (like
French) the construction will not work: the translation of the word
"full" depends on the gender of the first part of the sentence; it
happens to be not the same for "disk" as for "floppy disk".
Complete sentences can be translated without problems:
printf (capacity > 5000000 ? gettext ("disk is full")
: gettext ("floppy disk is full"));
A similar problem appears at the level of sentence structure with
this code:
printf ("# Implicit rule search has%s been done.\n",
f->tried_implicit ? "" : " not");
Adding `gettext' calls to this code cannot give correct results for all
languages, because negation in some languages requires adding words at
more than one place in the sentence. By contrast, adding `gettext'
calls does the job straightforwardly if the code starts out like this:
printf (f->tried_implicit
? "# Implicit rule search has been done.\n",
: "# Implicit rule search has not been done.\n");
Another example is this one:
printf ("%d file%s processed", nfiles,
nfiles != 1 ? "s" : "");
The problem with this example is that it assumes that plurals are made
by adding `s'. If you apply gettext to the format string, like this,
printf (gettext ("%d file%s processed"), nfiles,
nfiles != 1 ? "s" : "");
the message can use different words, but it will still be forced to use
`s' for the plural. Here is a better way, with gettext being applied to
the two strings independently:
printf ((nfiles != 1 ? gettext ("%d files processed")
: gettext ("%d file processed")),
nfiles);
But this still doesn't work for languages like Polish, which has three
plural forms: one for nfiles == 1, one for nfiles == 2, 3, 4, 22, 23,
24, ... and one for the rest. The GNU `ngettext' function solves this
problem:
printf (ngettext ("%d files processed", "%d file processed", nfiles),
nfiles);
File: standards.info, Node: Character Set, Next: Quote Characters, Prev: Internationalization, Up: Writing C
5.9 Character Set
=================
Sticking to the ASCII character set (plain text, 7-bit characters) is
preferred in GNU source code comments, text documents, and other
contexts, unless there is good reason to do something else because of
the application domain. For example, if source code deals with the
French Revolutionary calendar, it is OK if its literal strings contain
accented characters in month names like "Flore'al". Also, it is OK
(but not required) to use non-ASCII characters to represent proper
names of contributors in change logs (*note Change Logs::).
If you need to use non-ASCII characters, you should normally stick
with one encoding, certainly within a single file. UTF-8 is likely to
be the best choice.
File: standards.info, Node: Quote Characters, Next: Mmap, Prev: Character Set, Up: Writing C
5.10 Quote Characters
=====================
In the C locale, the output of GNU programs should stick to plain ASCII
for quotation characters in messages to users: preferably 0x22 (`"') or
0x27 (`'') for both opening and closing quotes. Although GNU programs
traditionally used 0x60 (``') for opening and 0x27 (`'') for closing
quotes, nowadays quotes ``like this'' are typically rendered
asymmetrically, so quoting `"like this"' or `'like this'' typically
looks better.
It is ok, but not required, for GNU programs to generate
locale-specific quotes in non-C locales. For example:
printf (gettext ("Processing file '%s'..."), file);
Here, a French translation might cause `gettext' to return the string
`"Traitement de fichier < %s >..."', yielding quotes more appropriate
for a French locale.
Sometimes a program may need to use opening and closing quotes
directly. By convention, `gettext' translates the string `"`"' to the
opening quote and the string `"'"' to the closing quote, and a program
can use these translations. Generally, though, it is better to
translate quote characters in the context of longer strings.
If the output of your program is ever likely to be parsed by another
program, it is good to provide an option that makes this parsing
reliable. For example, you could escape special characters using
conventions from the C language or the Bourne shell. See for example
the option `--quoting-style' of GNU `ls'.
File: standards.info, Node: Mmap, Prev: Quote Characters, Up: Writing C
5.11 Mmap
=========
Don't assume that `mmap' either works on all files or fails for all
files. It may work on some files and fail on others.
The proper way to use `mmap' is to try it on the specific file for
which you want to use it--and if `mmap' doesn't work, fall back on
doing the job in another way using `read' and `write'.
The reason this precaution is needed is that the GNU kernel (the
HURD) provides a user-extensible file system, in which there can be many
different kinds of "ordinary files". Many of them support `mmap', but
some do not. It is important to make programs handle all these kinds
of files.
File: standards.info, Node: Documentation, Next: Managing Releases, Prev: Writing C, Up: Top
6 Documenting Programs
**********************
A GNU program should ideally come with full free documentation, adequate
for both reference and tutorial purposes. If the package can be
programmed or extended, the documentation should cover programming or
extending it, as well as just using it.
* Menu:
* GNU Manuals:: Writing proper manuals.
* Doc Strings and Manuals:: Compiling doc strings doesn't make a manual.
* Manual Structure Details:: Specific structure conventions.
* License for Manuals:: Writing the distribution terms for a manual.
* Manual Credits:: Giving credit to documentation contributors.
* Printed Manuals:: Mentioning the printed manual.
* NEWS File:: NEWS files supplement manuals.
* Change Logs:: Recording changes.
* Man Pages:: Man pages are secondary.
* Reading other Manuals:: How far you can go in learning
from other manuals.
File: standards.info, Node: GNU Manuals, Next: Doc Strings and Manuals, Up: Documentation
6.1 GNU Manuals
===============
The preferred document format for the GNU system is the Texinfo
formatting language. Every GNU package should (ideally) have
documentation in Texinfo both for reference and for learners. Texinfo
makes it possible to produce a good quality formatted book, using TeX,
and to generate an Info file. It is also possible to generate HTML
output from Texinfo source. See the Texinfo manual, either the
hardcopy, or the on-line version available through `info' or the Emacs
Info subsystem (`C-h i').
Nowadays some other formats such as Docbook and Sgmltexi can be
converted automatically into Texinfo. It is ok to produce the Texinfo
documentation by conversion this way, as long as it gives good results.
Make sure your manual is clear to a reader who knows nothing about
the topic and reads it straight through. This means covering basic
topics at the beginning, and advanced topics only later. This also
means defining every specialized term when it is first used.
Programmers tend to carry over the structure of the program as the
structure for its documentation. But this structure is not necessarily
good for explaining how to use the program; it may be irrelevant and
confusing for a user.
Instead, the right way to structure documentation is according to the
concepts and questions that a user will have in mind when reading it.
This principle applies at every level, from the lowest (ordering
sentences in a paragraph) to the highest (ordering of chapter topics
within the manual). Sometimes this structure of ideas matches the
structure of the implementation of the software being documented--but
often they are different. An important part of learning to write good
documentation is to learn to notice when you have unthinkingly
structured the documentation like the implementation, stop yourself,
and look for better alternatives.
For example, each program in the GNU system probably ought to be
documented in one manual; but this does not mean each program should
have its own manual. That would be following the structure of the
implementation, rather than the structure that helps the user
understand.
Instead, each manual should cover a coherent _topic_. For example,
instead of a manual for `diff' and a manual for `diff3', we have one
manual for "comparison of files" which covers both of those programs,
as well as `cmp'. By documenting these programs together, we can make
the whole subject clearer.
The manual which discusses a program should certainly document all of
the program's command-line options and all of its commands. It should
give examples of their use. But don't organize the manual as a list of
features. Instead, organize it logically, by subtopics. Address the
questions that a user will ask when thinking about the job that the
program does. Don't just tell the reader what each feature can do--say
what jobs it is good for, and show how to use it for those jobs.
Explain what is recommended usage, and what kinds of usage users should
avoid.
In general, a GNU manual should serve both as tutorial and reference.
It should be set up for convenient access to each topic through Info,
and for reading straight through (appendixes aside). A GNU manual
should give a good introduction to a beginner reading through from the
start, and should also provide all the details that hackers want. The
Bison manual is a good example of this--please take a look at it to see
what we mean.
That is not as hard as it first sounds. Arrange each chapter as a
logical breakdown of its topic, but order the sections, and write their
text, so that reading the chapter straight through makes sense. Do
likewise when structuring the book into chapters, and when structuring a
section into paragraphs. The watchword is, _at each point, address the
most fundamental and important issue raised by the preceding text._
If necessary, add extra chapters at the beginning of the manual which
are purely tutorial and cover the basics of the subject. These provide
the framework for a beginner to understand the rest of the manual. The
Bison manual provides a good example of how to do this.
To serve as a reference, a manual should have an Index that list all
the functions, variables, options, and important concepts that are part
of the program. One combined Index should do for a short manual, but
sometimes for a complex package it is better to use multiple indices.
The Texinfo manual includes advice on preparing good index entries, see
*note Making Index Entries: (texinfo)Index Entries, and see *note
Defining the Entries of an Index: (texinfo)Indexing Commands.
Don't use Unix man pages as a model for how to write GNU
documentation; most of them are terse, badly structured, and give
inadequate explanation of the underlying concepts. (There are, of
course, some exceptions.) Also, Unix man pages use a particular format
which is different from what we use in GNU manuals.
Please include an email address in the manual for where to report
bugs _in the text of the manual_.
Please do not use the term "pathname" that is used in Unix
documentation; use "file name" (two words) instead. We use the term
"path" only for search paths, which are lists of directory names.
Please do not use the term "illegal" to refer to erroneous input to
a computer program. Please use "invalid" for this, and reserve the
term "illegal" for activities prohibited by law.
Please do not write `()' after a function name just to indicate it
is a function. `foo ()' is not a function, it is a function call with
no arguments.
File: standards.info, Node: Doc Strings and Manuals, Next: Manual Structure Details, Prev: GNU Manuals, Up: Documentation
6.2 Doc Strings and Manuals
===========================
Some programming systems, such as Emacs, provide a documentation string
for each function, command or variable. You may be tempted to write a
reference manual by compiling the documentation strings and writing a
little additional text to go around them--but you must not do it. That
approach is a fundamental mistake. The text of well-written
documentation strings will be entirely wrong for a manual.
A documentation string needs to stand alone--when it appears on the
screen, there will be no other text to introduce or explain it.
Meanwhile, it can be rather informal in style.
The text describing a function or variable in a manual must not stand
alone; it appears in the context of a section or subsection. Other text
at the beginning of the section should explain some of the concepts, and
should often make some general points that apply to several functions or
variables. The previous descriptions of functions and variables in the
section will also have given information about the topic. A description
written to stand alone would repeat some of that information; this
redundancy looks bad. Meanwhile, the informality that is acceptable in
a documentation string is totally unacceptable in a manual.
The only good way to use documentation strings in writing a good
manual is to use them as a source of information for writing good text.
File: standards.info, Node: Manual Structure Details, Next: License for Manuals, Prev: Doc Strings and Manuals, Up: Documentation
6.3 Manual Structure Details
============================
The title page of the manual should state the version of the programs or
packages documented in the manual. The Top node of the manual should
also contain this information. If the manual is changing more
frequently than or independent of the program, also state a version
number for the manual in both of these places.
Each program documented in the manual should have a node named
`PROGRAM Invocation' or `Invoking PROGRAM'. This node (together with
its subnodes, if any) should describe the program's command line
arguments and how to run it (the sort of information people would look
for in a man page). Start with an `@example' containing a template for
all the options and arguments that the program uses.
Alternatively, put a menu item in some menu whose item name fits one
of the above patterns. This identifies the node which that item points
to as the node for this purpose, regardless of the node's actual name.
The `--usage' feature of the Info reader looks for such a node or
menu item in order to find the relevant text, so it is essential for
every Texinfo file to have one.
If one manual describes several programs, it should have such a node
for each program described in the manual.
File: standards.info, Node: License for Manuals, Next: Manual Credits, Prev: Manual Structure Details, Up: Documentation
6.4 License for Manuals
=======================
Please use the GNU Free Documentation License for all GNU manuals that
are more than a few pages long. Likewise for a collection of short
documents--you only need one copy of the GNU FDL for the whole
collection. For a single short document, you can use a very permissive
non-copyleft license, to avoid taking up space with a long license.
See `http://www.gnu.org/copyleft/fdl-howto.html' for more explanation
of how to employ the GFDL.
Note that it is not obligatory to include a copy of the GNU GPL or
GNU LGPL in a manual whose license is neither the GPL nor the LGPL. It
can be a good idea to include the program's license in a large manual;
in a short manual, whose size would be increased considerably by
including the program's license, it is probably better not to include
it.
File: standards.info, Node: Manual Credits, Next: Printed Manuals, Prev: License for Manuals, Up: Documentation
6.5 Manual Credits
==================
Please credit the principal human writers of the manual as the authors,
on the title page of the manual. If a company sponsored the work, thank
the company in a suitable place in the manual, but do not cite the
company as an author.
File: standards.info, Node: Printed Manuals, Next: NEWS File, Prev: Manual Credits, Up: Documentation
6.6 Printed Manuals
===================
The FSF publishes some GNU manuals in printed form. To encourage sales
of these manuals, the on-line versions of the manual should mention at
the very start that the printed manual is available and should point at
information for getting it--for instance, with a link to the page
`http://www.gnu.org/order/order.html'. This should not be included in
the printed manual, though, because there it is redundant.
It is also useful to explain in the on-line forms of the manual how
the user can print out the manual from the sources.
File: standards.info, Node: NEWS File, Next: Change Logs, Prev: Printed Manuals, Up: Documentation
6.7 The NEWS File
=================
In addition to its manual, the package should have a file named `NEWS'
which contains a list of user-visible changes worth mentioning. In
each new release, add items to the front of the file and identify the
version they pertain to. Don't discard old items; leave them in the
file after the newer items. This way, a user upgrading from any
previous version can see what is new.
If the `NEWS' file gets very long, move some of the older items into
a file named `ONEWS' and put a note at the end referring the user to
that file.
File: standards.info, Node: Change Logs, Next: Man Pages, Prev: NEWS File, Up: Documentation
6.8 Change Logs
===============
Keep a change log to describe all the changes made to program source
files. The purpose of this is so that people investigating bugs in the
future will know about the changes that might have introduced the bug.
Often a new bug can be found by looking at what was recently changed.
More importantly, change logs can help you eliminate conceptual
inconsistencies between different parts of a program, by giving you a
history of how the conflicting concepts arose and who they came from.
* Menu:
* Change Log Concepts::
* Style of Change Logs::
* Simple Changes::
* Conditional Changes::
* Indicating the Part Changed::
File: standards.info, Node: Change Log Concepts, Next: Style of Change Logs, Up: Change Logs
6.8.1 Change Log Concepts
-------------------------
You can think of the change log as a conceptual "undo list" which
explains how earlier versions were different from the current version.
People can see the current version; they don't need the change log to
tell them what is in it. What they want from a change log is a clear
explanation of how the earlier version differed.
The change log file is normally called `ChangeLog' and covers an
entire directory. Each directory can have its own change log, or a
directory can use the change log of its parent directory--it's up to
you.
Another alternative is to record change log information with a
version control system such as RCS or CVS. This can be converted
automatically to a `ChangeLog' file using `rcs2log'; in Emacs, the
command `C-x v a' (`vc-update-change-log') does the job.
There's no need to describe the full purpose of the changes or how
they work together. However, sometimes it is useful to write one line
to describe the overall purpose of a change or a batch of changes. If
you think that a change calls for explanation, you're probably right.
Please do explain it--but please put the full explanation in comments
in the code, where people will see it whenever they see the code. For
example, "New function" is enough for the change log when you add a
function, because there should be a comment before the function
definition to explain what it does.
In the past, we recommended not mentioning changes in non-software
files (manuals, help files, etc.) in change logs. However, we've been
advised that it is a good idea to include them, for the sake of
copyright records.
The easiest way to add an entry to `ChangeLog' is with the Emacs
command `M-x add-change-log-entry'. An entry should have an asterisk,
the name of the changed file, and then in parentheses the name of the
changed functions, variables or whatever, followed by a colon. Then
describe the changes you made to that function or variable.
File: standards.info, Node: Style of Change Logs, Next: Simple Changes, Prev: Change Log Concepts, Up: Change Logs
6.8.2 Style of Change Logs
--------------------------
Here are some simple examples of change log entries, starting with the
header line that says who made the change and when it was installed,
followed by descriptions of specific changes. (These examples are
drawn from Emacs and GCC.)
1998-08-17 Richard Stallman
* register.el (insert-register): Return nil.
(jump-to-register): Likewise.
* sort.el (sort-subr): Return nil.
* tex-mode.el (tex-bibtex-file, tex-file, tex-region):
Restart the tex shell if process is gone or stopped.
(tex-shell-running): New function.
* expr.c (store_one_arg): Round size up for move_block_to_reg.
(expand_call): Round up when emitting USE insns.
* stmt.c (assign_parms): Round size up for move_block_from_reg.
It's important to name the changed function or variable in full.
Don't abbreviate function or variable names, and don't combine them.
Subsequent maintainers will often search for a function name to find all
the change log entries that pertain to it; if you abbreviate the name,
they won't find it when they search.
For example, some people are tempted to abbreviate groups of function
names by writing `* register.el ({insert,jump-to}-register)'; this is
not a good idea, since searching for `jump-to-register' or
`insert-register' would not find that entry.
Separate unrelated change log entries with blank lines. When two
entries represent parts of the same change, so that they work together,
then don't put blank lines between them. Then you can omit the file
name and the asterisk when successive entries are in the same file.
Break long lists of function names by closing continued lines with
`)', rather than `,', and opening the continuation with `(' as in this
example:
* keyboard.c (menu_bar_items, tool_bar_items)
(Fexecute_extended_command): Deal with 'keymap' property.
When you install someone else's changes, put the contributor's name
in the change log entry rather than in the text of the entry. In other
words, write this:
2002-07-14 John Doe
* sewing.c: Make it sew.
rather than this:
2002-07-14 Usual Maintainer
* sewing.c: Make it sew. Patch by jdoe@gnu.org.
As for the date, that should be the date you applied the change.
File: standards.info, Node: Simple Changes, Next: Conditional Changes, Prev: Style of Change Logs, Up: Change Logs
6.8.3 Simple Changes
--------------------
Certain simple kinds of changes don't need much detail in the change
log.
When you change the calling sequence of a function in a simple
fashion, and you change all the callers of the function to use the new
calling sequence, there is no need to make individual entries for all
the callers that you changed. Just write in the entry for the function
being called, "All callers changed"--like this:
* keyboard.c (Fcommand_execute): New arg SPECIAL.
All callers changed.
When you change just comments or doc strings, it is enough to write
an entry for the file, without mentioning the functions. Just "Doc
fixes" is enough for the change log.
There's no technical need to make change log entries for
documentation files. This is because documentation is not susceptible
to bugs that are hard to fix. Documentation does not consist of parts
that must interact in a precisely engineered fashion. To correct an
error, you need not know the history of the erroneous passage; it is
enough to compare what the documentation says with the way the program
actually works.
However, you should keep change logs for documentation files when the
project gets copyright assignments from its contributors, so as to make
the records of authorship more accurate.
File: standards.info, Node: Conditional Changes, Next: Indicating the Part Changed, Prev: Simple Changes, Up: Change Logs
6.8.4 Conditional Changes
-------------------------
Source files can often contain code that is conditional to build-time
or static conditions. For example, C programs can contain compile-time
`#if' conditionals; programs implemented in interpreted languages can
contain module imports of function definitions that are only performed
for certain versions of the interpreter; and Automake `Makefile.am'
files can contain variable definitions or target declarations that are
only to be considered if a configure-time Automake conditional is true.
Many changes are conditional as well: sometimes you add a new
variable, or function, or even a new program or library, which is
entirely dependent on a build-time condition. It is useful to indicate
in the change log the conditions for which a change applies.
Our convention for indicating conditional changes is to use _square
brackets around the name of the condition_.
Conditional changes can happen in numerous scenarios and with many
variations, so here are some examples to help clarify. This first
example describes changes in C, Perl, and Python files which are
conditional but do not have an associated function or entity name:
* xterm.c [SOLARIS2]: Include .
* FilePath.pm [$^O eq 'VMS']: Import the VMS::Feature module.
* framework.py [sys.version_info < (2, 6)]: Make "with" statement
available by importing it from __future__,
to support also python 2.5.
Our other examples will for simplicity be limited to C, as the minor
changes necessary to adapt them to other languages should be
self-evident.
Next, here is an entry describing a new definition which is entirely
conditional: the C macro `FRAME_WINDOW_P' is defined (and used) only
when the macro `HAVE_X_WINDOWS' is defined:
* frame.h [HAVE_X_WINDOWS] (FRAME_WINDOW_P): Macro defined.
Next, an entry for a change within the function `init_display',
whose definition as a whole is unconditional, but the changes
themselves are contained in a `#ifdef HAVE_LIBNCURSES' conditional:
* dispnew.c (init_display) [HAVE_LIBNCURSES]: If X, call tgetent.
Finally, here is an entry for a change that takes effect only when a
certain macro is _not_ defined:
(gethostname) [!HAVE_SOCKETS]: Replace with winsock version.
File: standards.info, Node: Indicating the Part Changed, Prev: Conditional Changes, Up: Change Logs
6.8.5 Indicating the Part Changed
---------------------------------
Indicate the part of a function which changed by using angle brackets
enclosing an indication of what the changed part does. Here is an entry
for a change in the part of the function `sh-while-getopts' that deals
with `sh' commands:
* progmodes/sh-script.el (sh-while-getopts) : Handle case that
user-specified option string is empty.
File: standards.info, Node: Man Pages, Next: Reading other Manuals, Prev: Change Logs, Up: Documentation
6.9 Man Pages
=============
In the GNU project, man pages are secondary. It is not necessary or
expected for every GNU program to have a man page, but some of them do.
It's your choice whether to include a man page in your program.
When you make this decision, consider that supporting a man page
requires continual effort each time the program is changed. The time
you spend on the man page is time taken away from more useful work.
For a simple program which changes little, updating the man page may
be a small job. Then there is little reason not to include a man page,
if you have one.
For a large program that changes a great deal, updating a man page
may be a substantial burden. If a user offers to donate a man page,
you may find this gift costly to accept. It may be better to refuse
the man page unless the same person agrees to take full responsibility
for maintaining it--so that you can wash your hands of it entirely. If
this volunteer later ceases to do the job, then don't feel obliged to
pick it up yourself; it may be better to withdraw the man page from the
distribution until someone else agrees to update it.
When a program changes only a little, you may feel that the
discrepancies are small enough that the man page remains useful without
updating. If so, put a prominent note near the beginning of the man
page explaining that you don't maintain it and that the Texinfo manual
is more authoritative. The note should say how to access the Texinfo
documentation.
Be sure that man pages include a copyright statement and free
license. The simple all-permissive license is appropriate for simple
man pages (*note License Notices for Other Files: (maintain)License
Notices for Other Files.).
For long man pages, with enough explanation and documentation that
they can be considered true manuals, use the GFDL (*note License for
Manuals::).
Finally, the GNU help2man program
(`http://www.gnu.org/software/help2man/') is one way to automate
generation of a man page, in this case from `--help' output. This is
sufficient in many cases.
File: standards.info, Node: Reading other Manuals, Prev: Man Pages, Up: Documentation
6.10 Reading other Manuals
==========================
There may be non-free books or documentation files that describe the
program you are documenting.
It is ok to use these documents for reference, just as the author of
a new algebra textbook can read other books on algebra. A large portion
of any non-fiction book consists of facts, in this case facts about how
a certain program works, and these facts are necessarily the same for
everyone who writes about the subject. But be careful not to copy your
outline structure, wording, tables or examples from preexisting non-free
documentation. Copying from free documentation may be ok; please check
with the FSF about the individual case.
File: standards.info, Node: Managing Releases, Next: References, Prev: Documentation, Up: Top
7 The Release Process
*********************
Making a release is more than just bundling up your source files in a
tar file and putting it up for FTP. You should set up your software so
that it can be configured to run on a variety of systems. Your Makefile
should conform to the GNU standards described below, and your directory
layout should also conform to the standards discussed below. Doing so
makes it easy to include your package into the larger framework of all
GNU software.
* Menu:
* Configuration:: How configuration of GNU packages should work.
* Makefile Conventions:: Makefile conventions.
* Releases:: Making releases
File: standards.info, Node: Configuration, Next: Makefile Conventions, Up: Managing Releases
7.1 How Configuration Should Work
=================================
Each GNU distribution should come with a shell script named
`configure'. This script is given arguments which describe the kind of
machine and system you want to compile the program for. The
`configure' script must record the configuration options so that they
affect compilation.
The description here is the specification of the interface for the
`configure' script in GNU packages. Many packages implement it using
GNU Autoconf (*note Introduction: (autoconf)Top.) and/or GNU Automake
(*note Introduction: (automake)Top.), but you do not have to use these
tools. You can implement it any way you like; for instance, by making
`configure' be a wrapper around a completely different configuration
system.
Another way for the `configure' script to operate is to make a link
from a standard name such as `config.h' to the proper configuration
file for the chosen system. If you use this technique, the
distribution should _not_ contain a file named `config.h'. This is so
that people won't be able to build the program without configuring it
first.
Another thing that `configure' can do is to edit the Makefile. If
you do this, the distribution should _not_ contain a file named
`Makefile'. Instead, it should include a file `Makefile.in' which
contains the input used for editing. Once again, this is so that people
won't be able to build the program without configuring it first.
If `configure' does write the `Makefile', then `Makefile' should
have a target named `Makefile' which causes `configure' to be rerun,
setting up the same configuration that was set up last time. The files
that `configure' reads should be listed as dependencies of `Makefile'.
All the files which are output from the `configure' script should
have comments at the beginning explaining that they were generated
automatically using `configure'. This is so that users won't think of
trying to edit them by hand.
The `configure' script should write a file named `config.status'
which describes which configuration options were specified when the
program was last configured. This file should be a shell script which,
if run, will recreate the same configuration.
The `configure' script should accept an option of the form
`--srcdir=DIRNAME' to specify the directory where sources are found (if
it is not the current directory). This makes it possible to build the
program in a separate directory, so that the actual source directory is
not modified.
If the user does not specify `--srcdir', then `configure' should
check both `.' and `..' to see if it can find the sources. If it finds
the sources in one of these places, it should use them from there.
Otherwise, it should report that it cannot find the sources, and should
exit with nonzero status.
Usually the easy way to support `--srcdir' is by editing a
definition of `VPATH' into the Makefile. Some rules may need to refer
explicitly to the specified source directory. To make this possible,
`configure' can add to the Makefile a variable named `srcdir' whose
value is precisely the specified directory.
In addition, the `configure' script should take options
corresponding to most of the standard directory variables (*note
Directory Variables::). Here is the list:
--prefix --exec-prefix --bindir --sbindir --libexecdir --sysconfdir
--sharedstatedir --localstatedir --libdir --includedir --oldincludedir
--datarootdir --datadir --infodir --localedir --mandir --docdir
--htmldir --dvidir --pdfdir --psdir
The `configure' script should also take an argument which specifies
the type of system to build the program for. This argument should look
like this:
CPU-COMPANY-SYSTEM
For example, an Athlon-based GNU/Linux system might be
`i686-pc-linux-gnu'.
The `configure' script needs to be able to decode all plausible
alternatives for how to describe a machine. Thus,
`athlon-pc-gnu/linux' would be a valid alias. There is a shell script
called `config.sub'
(http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.sub;hb=HEAD)
that you can use as a subroutine to validate system types and
canonicalize aliases.
The `configure' script should also take the option
`--build=BUILDTYPE', which should be equivalent to a plain BUILDTYPE
argument. For example, `configure --build=i686-pc-linux-gnu' is
equivalent to `configure i686-pc-linux-gnu'. When the build type is
not specified by an option or argument, the `configure' script should
normally guess it using the shell script `config.guess'
(http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.guess;hb=HEAD).
Other options are permitted to specify in more detail the software
or hardware present on the machine, to include or exclude optional parts
of the package, or to adjust the name of some tools or arguments to
them:
`--enable-FEATURE[=PARAMETER]'
Configure the package to build and install an optional user-level
facility called FEATURE. This allows users to choose which
optional features to include. Giving an optional PARAMETER of
`no' should omit FEATURE, if it is built by default.
No `--enable' option should *ever* cause one feature to replace
another. No `--enable' option should ever substitute one useful
behavior for another useful behavior. The only proper use for
`--enable' is for questions of whether to build part of the program
or exclude it.
`--with-PACKAGE'
The package PACKAGE will be installed, so configure this package
to work with PACKAGE.
Possible values of PACKAGE include `gnu-as' (or `gas'), `gnu-ld',
`gnu-libc', `gdb', `x', and `x-toolkit'.
Do not use a `--with' option to specify the file name to use to
find certain files. That is outside the scope of what `--with'
options are for.
`VARIABLE=VALUE'
Set the value of the variable VARIABLE to VALUE. This is used to
override the default values of commands or arguments in the build
process. For example, the user could issue `configure CFLAGS=-g
CXXFLAGS=-g' to build with debugging information and without the
default optimization.
Specifying variables as arguments to `configure', like this:
./configure CC=gcc
is preferable to setting them in environment variables:
CC=gcc ./configure
as it helps to recreate the same configuration later with
`config.status'. However, both methods should be supported.
All `configure' scripts should accept all of the "detail" options
and the variable settings, whether or not they make any difference to
the particular package at hand. In particular, they should accept any
option that starts with `--with-' or `--enable-'. This is so users
will be able to configure an entire GNU source tree at once with a
single set of options.
You will note that the categories `--with-' and `--enable-' are
narrow: they *do not* provide a place for any sort of option you might
think of. That is deliberate. We want to limit the possible
configuration options in GNU software. We do not want GNU programs to
have idiosyncratic configuration options.
Packages that perform part of the compilation process may support
cross-compilation. In such a case, the host and target machines for the
program may be different.
The `configure' script should normally treat the specified type of
system as both the host and the target, thus producing a program which
works for the same type of machine that it runs on.
To compile a program to run on a host type that differs from the
build type, use the configure option `--host=HOSTTYPE', where HOSTTYPE
uses the same syntax as BUILDTYPE. The host type normally defaults to
the build type.
To configure a cross-compiler, cross-assembler, or what have you, you
should specify a target different from the host, using the configure
option `--target=TARGETTYPE'. The syntax for TARGETTYPE is the same as
for the host type. So the command would look like this:
./configure --host=HOSTTYPE --target=TARGETTYPE
The target type normally defaults to the host type. Programs for
which cross-operation is not meaningful need not accept the `--target'
option, because configuring an entire operating system for
cross-operation is not a meaningful operation.
Some programs have ways of configuring themselves automatically. If
your program is set up to do this, your `configure' script can simply
ignore most of its arguments.
File: standards.info, Node: Makefile Conventions, Next: Releases, Prev: Configuration, Up: Managing Releases
7.2 Makefile Conventions
========================
This node describes conventions for writing the Makefiles for GNU
programs. Using Automake will help you write a Makefile that follows
these conventions. For more information on portable Makefiles, see
POSIX and *note Portable Make Programming: (autoconf)Portable Make.
* Menu:
* Makefile Basics:: General conventions for Makefiles.
* Utilities in Makefiles:: Utilities to be used in Makefiles.
* Command Variables:: Variables for specifying commands.
* DESTDIR:: Supporting staged installs.
* Directory Variables:: Variables for installation directories.
* Standard Targets:: Standard targets for users.
* Install Command Categories:: Three categories of commands in the `install'
rule: normal, pre-install and post-install.
File: standards.info, Node: Makefile Basics, Next: Utilities in Makefiles, Up: Makefile Conventions
7.2.1 General Conventions for Makefiles
---------------------------------------
Every Makefile should contain this line:
SHELL = /bin/sh
to avoid trouble on systems where the `SHELL' variable might be
inherited from the environment. (This is never a problem with GNU
`make'.)
Different `make' programs have incompatible suffix lists and
implicit rules, and this sometimes creates confusion or misbehavior. So
it is a good idea to set the suffix list explicitly using only the
suffixes you need in the particular Makefile, like this:
.SUFFIXES:
.SUFFIXES: .c .o
The first line clears out the suffix list, the second introduces all
suffixes which may be subject to implicit rules in this Makefile.
Don't assume that `.' is in the path for command execution. When
you need to run programs that are a part of your package during the
make, please make sure that it uses `./' if the program is built as
part of the make or `$(srcdir)/' if the file is an unchanging part of
the source code. Without one of these prefixes, the current search
path is used.
The distinction between `./' (the "build directory") and
`$(srcdir)/' (the "source directory") is important because users can
build in a separate directory using the `--srcdir' option to
`configure'. A rule of the form:
foo.1 : foo.man sedscript
sed -f sedscript foo.man > foo.1
will fail when the build directory is not the source directory, because
`foo.man' and `sedscript' are in the source directory.
When using GNU `make', relying on `VPATH' to find the source file
will work in the case where there is a single dependency file, since
the `make' automatic variable `$ $@
GNU distributions usually contain some files which are not source
files--for example, Info files, and the output from Autoconf, Automake,
Bison or Flex. Since these files normally appear in the source
directory, they should always appear in the source directory, not in the
build directory. So Makefile rules to update them should put the
updated files in the source directory.
However, if a file does not appear in the distribution, then the
Makefile should not put it in the source directory, because building a
program in ordinary circumstances should not modify the source directory
in any way.
Try to make the build and installation targets, at least (and all
their subtargets) work correctly with a parallel `make'.
File: standards.info, Node: Utilities in Makefiles, Next: Command Variables, Prev: Makefile Basics, Up: Makefile Conventions
7.2.2 Utilities in Makefiles
----------------------------
Write the Makefile commands (and any shell scripts, such as
`configure') to run under `sh' (both the traditional Bourne shell and
the POSIX shell), not `csh'. Don't use any special features of `ksh'
or `bash', or POSIX features not widely supported in traditional Bourne
`sh'.
The `configure' script and the Makefile rules for building and
installation should not use any utilities directly except these:
awk cat cmp cp diff echo egrep expr false grep install-info ln ls
mkdir mv printf pwd rm rmdir sed sleep sort tar test touch tr true
Compression programs such as `gzip' can be used in the `dist' rule.
Generally, stick to the widely-supported (usually POSIX-specified)
options and features of these programs. For example, don't use `mkdir
-p', convenient as it may be, because a few systems don't support it at
all and with others, it is not safe for parallel execution. For a list
of known incompatibilities, see *note Portable Shell Programming:
(autoconf)Portable Shell.
It is a good idea to avoid creating symbolic links in makefiles,
since a few file systems don't support them.
The Makefile rules for building and installation can also use
compilers and related programs, but should do so via `make' variables
so that the user can substitute alternatives. Here are some of the
programs we mean:
ar bison cc flex install ld ldconfig lex
make makeinfo ranlib texi2dvi yacc
Use the following `make' variables to run those programs:
$(AR) $(BISON) $(CC) $(FLEX) $(INSTALL) $(LD) $(LDCONFIG) $(LEX)
$(MAKE) $(MAKEINFO) $(RANLIB) $(TEXI2DVI) $(YACC)
When you use `ranlib' or `ldconfig', you should make sure nothing
bad happens if the system does not have the program in question.
Arrange to ignore an error from that command, and print a message before
the command to tell the user that failure of this command does not mean
a problem. (The Autoconf `AC_PROG_RANLIB' macro can help with this.)
If you use symbolic links, you should implement a fallback for
systems that don't have symbolic links.
Additional utilities that can be used via Make variables are:
chgrp chmod chown mknod
It is ok to use other utilities in Makefile portions (or scripts)
intended only for particular systems where you know those utilities
exist.
File: standards.info, Node: Command Variables, Next: DESTDIR, Prev: Utilities in Makefiles, Up: Makefile Conventions
7.2.3 Variables for Specifying Commands
---------------------------------------
Makefiles should provide variables for overriding certain commands,
options, and so on.
In particular, you should run most utility programs via variables.
Thus, if you use Bison, have a variable named `BISON' whose default
value is set with `BISON = bison', and refer to it with `$(BISON)'
whenever you need to use Bison.
File management utilities such as `ln', `rm', `mv', and so on, need
not be referred to through variables in this way, since users don't
need to replace them with other programs.
Each program-name variable should come with an options variable that
is used to supply options to the program. Append `FLAGS' to the
program-name variable name to get the options variable name--for
example, `BISONFLAGS'. (The names `CFLAGS' for the C compiler,
`YFLAGS' for yacc, and `LFLAGS' for lex, are exceptions to this rule,
but we keep them because they are standard.) Use `CPPFLAGS' in any
compilation command that runs the preprocessor, and use `LDFLAGS' in
any compilation command that does linking as well as in any direct use
of `ld'.
If there are C compiler options that _must_ be used for proper
compilation of certain files, do not include them in `CFLAGS'. Users
expect to be able to specify `CFLAGS' freely themselves. Instead,
arrange to pass the necessary options to the C compiler independently
of `CFLAGS', by writing them explicitly in the compilation commands or
by defining an implicit rule, like this:
CFLAGS = -g
ALL_CFLAGS = -I. $(CFLAGS)
.c.o:
$(CC) -c $(CPPFLAGS) $(ALL_CFLAGS) $<
Do include the `-g' option in `CFLAGS', because that is not
_required_ for proper compilation. You can consider it a default that
is only recommended. If the package is set up so that it is compiled
with GCC by default, then you might as well include `-O' in the default
value of `CFLAGS' as well.
Put `CFLAGS' last in the compilation command, after other variables
containing compiler options, so the user can use `CFLAGS' to override
the others.
`CFLAGS' should be used in every invocation of the C compiler, both
those which do compilation and those which do linking.
Every Makefile should define the variable `INSTALL', which is the
basic command for installing a file into the system.
Every Makefile should also define the variables `INSTALL_PROGRAM'
and `INSTALL_DATA'. (The default for `INSTALL_PROGRAM' should be
`$(INSTALL)'; the default for `INSTALL_DATA' should be `${INSTALL} -m
644'.) Then it should use those variables as the commands for actual
installation, for executables and non-executables respectively.
Minimal use of these variables is as follows:
$(INSTALL_PROGRAM) foo $(bindir)/foo
$(INSTALL_DATA) libfoo.a $(libdir)/libfoo.a
However, it is preferable to support a `DESTDIR' prefix on the
target files, as explained in the next section.
It is acceptable, but not required, to install multiple files in one
command, with the final argument being a directory, as in:
$(INSTALL_PROGRAM) foo bar baz $(bindir)
File: standards.info, Node: DESTDIR, Next: Directory Variables, Prev: Command Variables, Up: Makefile Conventions
7.2.4 `DESTDIR': Support for Staged Installs
--------------------------------------------
`DESTDIR' is a variable prepended to each installed target file, like
this:
$(INSTALL_PROGRAM) foo $(DESTDIR)$(bindir)/foo
$(INSTALL_DATA) libfoo.a $(DESTDIR)$(libdir)/libfoo.a
The `DESTDIR' variable is specified by the user on the `make'
command line as an absolute file name. For example:
make DESTDIR=/tmp/stage install
`DESTDIR' should be supported only in the `install*' and `uninstall*'
targets, as those are the only targets where it is useful.
If your installation step would normally install
`/usr/local/bin/foo' and `/usr/local/lib/libfoo.a', then an
installation invoked as in the example above would install
`/tmp/stage/usr/local/bin/foo' and `/tmp/stage/usr/local/lib/libfoo.a'
instead.
Prepending the variable `DESTDIR' to each target in this way
provides for "staged installs", where the installed files are not
placed directly into their expected location but are instead copied
into a temporary location (`DESTDIR'). However, installed files
maintain their relative directory structure and any embedded file names
will not be modified.
You should not set the value of `DESTDIR' in your `Makefile' at all;
then the files are installed into their expected locations by default.
Also, specifying `DESTDIR' should not change the operation of the
software in any way, so its value should not be included in any file
contents.
`DESTDIR' support is commonly used in package creation. It is also
helpful to users who want to understand what a given package will
install where, and to allow users who don't normally have permissions
to install into protected areas to build and install before gaining
those permissions. Finally, it can be useful with tools such as
`stow', where code is installed in one place but made to appear to be
installed somewhere else using symbolic links or special mount
operations. So, we strongly recommend GNU packages support `DESTDIR',
though it is not an absolute requirement.
File: standards.info, Node: Directory Variables, Next: Standard Targets, Prev: DESTDIR, Up: Makefile Conventions
7.2.5 Variables for Installation Directories
--------------------------------------------
Installation directories should always be named by variables, so it is
easy to install in a nonstandard place. The standard names for these
variables and the values they should have in GNU packages are described
below. They are based on a standard file system layout; variants of it
are used in GNU/Linux and other modern operating systems.
Installers are expected to override these values when calling `make'
(e.g., `make prefix=/usr install' or `configure' (e.g., `configure
--prefix=/usr'). GNU packages should not try to guess which value
should be appropriate for these variables on the system they are being
installed onto: use the default settings specified here so that all GNU
packages behave identically, allowing the installer to achieve any
desired layout.
All installation directories, and their parent directories, should be
created (if necessary) before they are installed into.
These first two variables set the root for the installation. All the
other installation directories should be subdirectories of one of these
two, and nothing should be directly installed into these two
directories.
`prefix'
A prefix used in constructing the default values of the variables
listed below. The default value of `prefix' should be
`/usr/local'. When building the complete GNU system, the prefix
will be empty and `/usr' will be a symbolic link to `/'. (If you
are using Autoconf, write it as `@prefix@'.)
Running `make install' with a different value of `prefix' from the
one used to build the program should _not_ recompile the program.
`exec_prefix'
A prefix used in constructing the default values of some of the
variables listed below. The default value of `exec_prefix' should
be `$(prefix)'. (If you are using Autoconf, write it as
`@exec_prefix@'.)
Generally, `$(exec_prefix)' is used for directories that contain
machine-specific files (such as executables and subroutine
libraries), while `$(prefix)' is used directly for other
directories.
Running `make install' with a different value of `exec_prefix'
from the one used to build the program should _not_ recompile the
program.
Executable programs are installed in one of the following
directories.
`bindir'
The directory for installing executable programs that users can
run. This should normally be `/usr/local/bin', but write it as
`$(exec_prefix)/bin'. (If you are using Autoconf, write it as
`@bindir@'.)
`sbindir'
The directory for installing executable programs that can be run
from the shell, but are only generally useful to system
administrators. This should normally be `/usr/local/sbin', but
write it as `$(exec_prefix)/sbin'. (If you are using Autoconf,
write it as `@sbindir@'.)
`libexecdir'
The directory for installing executable programs to be run by other
programs rather than by users. This directory should normally be
`/usr/local/libexec', but write it as `$(exec_prefix)/libexec'.
(If you are using Autoconf, write it as `@libexecdir@'.)
The definition of `libexecdir' is the same for all packages, so
you should install your data in a subdirectory thereof. Most
packages install their data under `$(libexecdir)/PACKAGE-NAME/',
possibly within additional subdirectories thereof, such as
`$(libexecdir)/PACKAGE-NAME/MACHINE/VERSION'.
Data files used by the program during its execution are divided into
categories in two ways.
* Some files are normally modified by programs; others are never
normally modified (though users may edit some of these).
* Some files are architecture-independent and can be shared by all
machines at a site; some are architecture-dependent and can be
shared only by machines of the same kind and operating system;
others may never be shared between two machines.
This makes for six different possibilities. However, we want to
discourage the use of architecture-dependent files, aside from object
files and libraries. It is much cleaner to make other data files
architecture-independent, and it is generally not hard.
Here are the variables Makefiles should use to specify directories
to put these various kinds of files in:
`datarootdir'
The root of the directory tree for read-only
architecture-independent data files. This should normally be
`/usr/local/share', but write it as `$(prefix)/share'. (If you
are using Autoconf, write it as `@datarootdir@'.) `datadir''s
default value is based on this variable; so are `infodir',
`mandir', and others.
`datadir'
The directory for installing idiosyncratic read-only
architecture-independent data files for this program. This is
usually the same place as `datarootdir', but we use the two
separate variables so that you can move these program-specific
files without altering the location for Info files, man pages, etc.
This should normally be `/usr/local/share', but write it as
`$(datarootdir)'. (If you are using Autoconf, write it as
`@datadir@'.)
The definition of `datadir' is the same for all packages, so you
should install your data in a subdirectory thereof. Most packages
install their data under `$(datadir)/PACKAGE-NAME/'.
`sysconfdir'
The directory for installing read-only data files that pertain to a
single machine-that is to say, files for configuring a host.
Mailer and network configuration files, `/etc/passwd', and so
forth belong here. All the files in this directory should be
ordinary ASCII text files. This directory should normally be
`/usr/local/etc', but write it as `$(prefix)/etc'. (If you are
using Autoconf, write it as `@sysconfdir@'.)
Do not install executables here in this directory (they probably
belong in `$(libexecdir)' or `$(sbindir)'). Also do not install
files that are modified in the normal course of their use (programs
whose purpose is to change the configuration of the system
excluded). Those probably belong in `$(localstatedir)'.
`sharedstatedir'
The directory for installing architecture-independent data files
which the programs modify while they run. This should normally be
`/usr/local/com', but write it as `$(prefix)/com'. (If you are
using Autoconf, write it as `@sharedstatedir@'.)
`localstatedir'
The directory for installing data files which the programs modify
while they run, and that pertain to one specific machine. Users
should never need to modify files in this directory to configure
the package's operation; put such configuration information in
separate files that go in `$(datadir)' or `$(sysconfdir)'.
`$(localstatedir)' should normally be `/usr/local/var', but write
it as `$(prefix)/var'. (If you are using Autoconf, write it as
`@localstatedir@'.)
These variables specify the directory for installing certain specific
types of files, if your program has them. Every GNU package should
have Info files, so every program needs `infodir', but not all need
`libdir' or `lispdir'.
`includedir'
The directory for installing header files to be included by user
programs with the C `#include' preprocessor directive. This
should normally be `/usr/local/include', but write it as
`$(prefix)/include'. (If you are using Autoconf, write it as
`@includedir@'.)
Most compilers other than GCC do not look for header files in
directory `/usr/local/include'. So installing the header files
this way is only useful with GCC. Sometimes this is not a problem
because some libraries are only really intended to work with GCC.
But some libraries are intended to work with other compilers.
They should install their header files in two places, one
specified by `includedir' and one specified by `oldincludedir'.
`oldincludedir'
The directory for installing `#include' header files for use with
compilers other than GCC. This should normally be `/usr/include'.
(If you are using Autoconf, you can write it as `@oldincludedir@'.)
The Makefile commands should check whether the value of
`oldincludedir' is empty. If it is, they should not try to use
it; they should cancel the second installation of the header files.
A package should not replace an existing header in this directory
unless the header came from the same package. Thus, if your Foo
package provides a header file `foo.h', then it should install the
header file in the `oldincludedir' directory if either (1) there
is no `foo.h' there or (2) the `foo.h' that exists came from the
Foo package.
To tell whether `foo.h' came from the Foo package, put a magic
string in the file--part of a comment--and `grep' for that string.
`docdir'
The directory for installing documentation files (other than Info)
for this package. By default, it should be
`/usr/local/share/doc/YOURPKG', but it should be written as
`$(datarootdir)/doc/YOURPKG'. (If you are using Autoconf, write
it as `@docdir@'.) The YOURPKG subdirectory, which may include a
version number, prevents collisions among files with common names,
such as `README'.
`infodir'
The directory for installing the Info files for this package. By
default, it should be `/usr/local/share/info', but it should be
written as `$(datarootdir)/info'. (If you are using Autoconf,
write it as `@infodir@'.) `infodir' is separate from `docdir' for
compatibility with existing practice.
`htmldir'
`dvidir'
`pdfdir'
`psdir'
Directories for installing documentation files in the particular
format. They should all be set to `$(docdir)' by default. (If
you are using Autoconf, write them as `@htmldir@', `@dvidir@',
etc.) Packages which supply several translations of their
documentation should install them in `$(htmldir)/'LL,
`$(pdfdir)/'LL, etc. where LL is a locale abbreviation such as
`en' or `pt_BR'.
`libdir'
The directory for object files and libraries of object code. Do
not install executables here, they probably ought to go in
`$(libexecdir)' instead. The value of `libdir' should normally be
`/usr/local/lib', but write it as `$(exec_prefix)/lib'. (If you
are using Autoconf, write it as `@libdir@'.)
`lispdir'
The directory for installing any Emacs Lisp files in this package.
By default, it should be `/usr/local/share/emacs/site-lisp', but it
should be written as `$(datarootdir)/emacs/site-lisp'.
If you are using Autoconf, write the default as `@lispdir@'. In
order to make `@lispdir@' work, you need the following lines in
your `configure.in' file:
lispdir='${datarootdir}/emacs/site-lisp'
AC_SUBST(lispdir)
`localedir'
The directory for installing locale-specific message catalogs for
this package. By default, it should be `/usr/local/share/locale',
but it should be written as `$(datarootdir)/locale'. (If you are
using Autoconf, write it as `@localedir@'.) This directory
usually has a subdirectory per locale.
Unix-style man pages are installed in one of the following:
`mandir'
The top-level directory for installing the man pages (if any) for
this package. It will normally be `/usr/local/share/man', but you
should write it as `$(datarootdir)/man'. (If you are using
Autoconf, write it as `@mandir@'.)
`man1dir'
The directory for installing section 1 man pages. Write it as
`$(mandir)/man1'.
`man2dir'
The directory for installing section 2 man pages. Write it as
`$(mandir)/man2'
`...'
*Don't make the primary documentation for any GNU software be a
man page. Write a manual in Texinfo instead. Man pages are just
for the sake of people running GNU software on Unix, which is a
secondary application only.*
`manext'
The file name extension for the installed man page. This should
contain a period followed by the appropriate digit; it should
normally be `.1'.
`man1ext'
The file name extension for installed section 1 man pages.
`man2ext'
The file name extension for installed section 2 man pages.
`...'
Use these names instead of `manext' if the package needs to
install man pages in more than one section of the manual.
And finally, you should set the following variable:
`srcdir'
The directory for the sources being compiled. The value of this
variable is normally inserted by the `configure' shell script.
(If you are using Autoconf, use `srcdir = @srcdir@'.)
For example:
# Common prefix for installation directories.
# NOTE: This directory must exist when you start the install.
prefix = /usr/local
datarootdir = $(prefix)/share
datadir = $(datarootdir)
exec_prefix = $(prefix)
# Where to put the executable for the command `gcc'.
bindir = $(exec_prefix)/bin
# Where to put the directories used by the compiler.
libexecdir = $(exec_prefix)/libexec
# Where to put the Info files.
infodir = $(datarootdir)/info
If your program installs a large number of files into one of the
standard user-specified directories, it might be useful to group them
into a subdirectory particular to that program. If you do this, you
should write the `install' rule to create these subdirectories.
Do not expect the user to include the subdirectory name in the value
of any of the variables listed above. The idea of having a uniform set
of variable names for installation directories is to enable the user to
specify the exact same values for several different GNU packages. In
order for this to be useful, all the packages must be designed so that
they will work sensibly when the user does so.
At times, not all of these variables may be implemented in the
current release of Autoconf and/or Automake; but as of Autoconf 2.60, we
believe all of them are. When any are missing, the descriptions here
serve as specifications for what Autoconf will implement. As a
programmer, you can either use a development version of Autoconf or
avoid using these variables until a stable release is made which
supports them.
File: standards.info, Node: Standard Targets, Next: Install Command Categories, Prev: Directory Variables, Up: Makefile Conventions
7.2.6 Standard Targets for Users
--------------------------------
All GNU programs should have the following targets in their Makefiles:
`all'
Compile the entire program. This should be the default target.
This target need not rebuild any documentation files; Info files
should normally be included in the distribution, and DVI (and other
documentation format) files should be made only when explicitly
asked for.
By default, the Make rules should compile and link with `-g', so
that executable programs have debugging symbols. Otherwise, you
are essentially helpless in the face of a crash, and it is often
far from easy to reproduce with a fresh build.
`install'
Compile the program and copy the executables, libraries, and so on
to the file names where they should reside for actual use. If
there is a simple test to verify that a program is properly
installed, this target should run that test.
Do not strip executables when installing them. This helps eventual
debugging that may be needed later, and nowadays disk space is
cheap and dynamic loaders typically ensure debug sections are not
loaded during normal execution. Users that need stripped binaries
may invoke the `install-strip' target to do that.
If possible, write the `install' target rule so that it does not
modify anything in the directory where the program was built,
provided `make all' has just been done. This is convenient for
building the program under one user name and installing it under
another.
The commands should create all the directories in which files are
to be installed, if they don't already exist. This includes the
directories specified as the values of the variables `prefix' and
`exec_prefix', as well as all subdirectories that are needed. One
way to do this is by means of an `installdirs' target as described
below.
Use `-' before any command for installing a man page, so that
`make' will ignore any errors. This is in case there are systems
that don't have the Unix man page documentation system installed.
The way to install Info files is to copy them into `$(infodir)'
with `$(INSTALL_DATA)' (*note Command Variables::), and then run
the `install-info' program if it is present. `install-info' is a
program that edits the Info `dir' file to add or update the menu
entry for the given Info file; it is part of the Texinfo package.
Here is a sample rule to install an Info file that also tries to
handle some additional situations, such as `install-info' not
being present.
do-install-info: foo.info installdirs
$(NORMAL_INSTALL)
# Prefer an info file in . to one in srcdir.
if test -f foo.info; then d=.; \
else d="$(srcdir)"; fi; \
$(INSTALL_DATA) $$d/foo.info \
"$(DESTDIR)$(infodir)/foo.info"
# Run install-info only if it exists.
# Use `if' instead of just prepending `-' to the
# line so we notice real errors from install-info.
# Use `$(SHELL) -c' because some shells do not
# fail gracefully when there is an unknown command.
$(POST_INSTALL)
if $(SHELL) -c 'install-info --version' \
>/dev/null 2>&1; then \
install-info --dir-file="$(DESTDIR)$(infodir)/dir" \
"$(DESTDIR)$(infodir)/foo.info"; \
else true; fi
When writing the `install' target, you must classify all the
commands into three categories: normal ones, "pre-installation"
commands and "post-installation" commands. *Note Install Command
Categories::.
`install-html'
`install-dvi'
`install-pdf'
`install-ps'
These targets install documentation in formats other than Info;
they're intended to be called explicitly by the person installing
the package, if that format is desired. GNU prefers Info files,
so these must be installed by the `install' target.
When you have many documentation files to install, we recommend
that you avoid collisions and clutter by arranging for these
targets to install in subdirectories of the appropriate
installation directory, such as `htmldir'. As one example, if
your package has multiple manuals, and you wish to install HTML
documentation with many files (such as the "split" mode output by
`makeinfo --html'), you'll certainly want to use subdirectories,
or two nodes with the same name in different manuals will
overwrite each other.
Please make these `install-FORMAT' targets invoke the commands for
the FORMAT target, for example, by making FORMAT a dependency.
`uninstall'
Delete all the installed files--the copies that the `install' and
`install-*' targets create.
This rule should not modify the directories where compilation is
done, only the directories where files are installed.
The uninstallation commands are divided into three categories,
just like the installation commands. *Note Install Command
Categories::.
`install-strip'
Like `install', but strip the executable files while installing
them. In simple cases, this target can use the `install' target in
a simple way:
install-strip:
$(MAKE) INSTALL_PROGRAM='$(INSTALL_PROGRAM) -s' \
install
But if the package installs scripts as well as real executables,
the `install-strip' target can't just refer to the `install'
target; it has to strip the executables but not the scripts.
`install-strip' should not strip the executables in the build
directory which are being copied for installation. It should only
strip the copies that are installed.
Normally we do not recommend stripping an executable unless you
are sure the program has no bugs. However, it can be reasonable
to install a stripped executable for actual execution while saving
the unstripped executable elsewhere in case there is a bug.
`clean'
Delete all files in the current directory that are normally
created by building the program. Also delete files in other
directories if they are created by this makefile. However, don't
delete the files that record the configuration. Also preserve
files that could be made by building, but normally aren't because
the distribution comes with them. There is no need to delete
parent directories that were created with `mkdir -p', since they
could have existed anyway.
Delete `.dvi' files here if they are not part of the distribution.
`distclean'
Delete all files in the current directory (or created by this
makefile) that are created by configuring or building the program.
If you have unpacked the source and built the program without
creating any other files, `make distclean' should leave only the
files that were in the distribution. However, there is no need to
delete parent directories that were created with `mkdir -p', since
they could have existed anyway.
`mostlyclean'
Like `clean', but may refrain from deleting a few files that people
normally don't want to recompile. For example, the `mostlyclean'
target for GCC does not delete `libgcc.a', because recompiling it
is rarely necessary and takes a lot of time.
`maintainer-clean'
Delete almost everything that can be reconstructed with this
Makefile. This typically includes everything deleted by
`distclean', plus more: C source files produced by Bison, tags
tables, Info files, and so on.
The reason we say "almost everything" is that running the command
`make maintainer-clean' should not delete `configure' even if
`configure' can be remade using a rule in the Makefile. More
generally, `make maintainer-clean' should not delete anything that
needs to exist in order to run `configure' and then begin to build
the program. Also, there is no need to delete parent directories
that were created with `mkdir -p', since they could have existed
anyway. These are the only exceptions; `maintainer-clean' should
delete everything else that can be rebuilt.
The `maintainer-clean' target is intended to be used by a
maintainer of the package, not by ordinary users. You may need
special tools to reconstruct some of the files that `make
maintainer-clean' deletes. Since these files are normally
included in the distribution, we don't take care to make them easy
to reconstruct. If you find you need to unpack the full
distribution again, don't blame us.
To help make users aware of this, the commands for the special
`maintainer-clean' target should start with these two:
@echo 'This command is intended for maintainers to use; it'
@echo 'deletes files that may need special tools to rebuild.'
`TAGS'
Update a tags table for this program.
`info'
Generate any Info files needed. The best way to write the rules
is as follows:
info: foo.info
foo.info: foo.texi chap1.texi chap2.texi
$(MAKEINFO) $(srcdir)/foo.texi
You must define the variable `MAKEINFO' in the Makefile. It should
run the `makeinfo' program, which is part of the Texinfo
distribution.
Normally a GNU distribution comes with Info files, and that means
the Info files are present in the source directory. Therefore,
the Make rule for an info file should update it in the source
directory. When users build the package, ordinarily Make will not
update the Info files because they will already be up to date.
`dvi'
`html'
`pdf'
`ps'
Generate documentation files in the given format. These targets
should always exist, but any or all can be a no-op if the given
output format cannot be generated. These targets should not be
dependencies of the `all' target; the user must manually invoke
them.
Here's an example rule for generating DVI files from Texinfo:
dvi: foo.dvi
foo.dvi: foo.texi chap1.texi chap2.texi
$(TEXI2DVI) $(srcdir)/foo.texi
You must define the variable `TEXI2DVI' in the Makefile. It
should run the program `texi2dvi', which is part of the Texinfo
distribution. (`texi2dvi' uses TeX to do the real work of
formatting. TeX is not distributed with Texinfo.) Alternatively,
write only the dependencies, and allow GNU `make' to provide the
command.
Here's another example, this one for generating HTML from Texinfo:
html: foo.html
foo.html: foo.texi chap1.texi chap2.texi
$(TEXI2HTML) $(srcdir)/foo.texi
Again, you would define the variable `TEXI2HTML' in the Makefile;
for example, it might run `makeinfo --no-split --html' (`makeinfo'
is part of the Texinfo distribution).
`dist'
Create a distribution tar file for this program. The tar file
should be set up so that the file names in the tar file start with
a subdirectory name which is the name of the package it is a
distribution for. This name can include the version number.
For example, the distribution tar file of GCC version 1.40 unpacks
into a subdirectory named `gcc-1.40'.
The easiest way to do this is to create a subdirectory
appropriately named, use `ln' or `cp' to install the proper files
in it, and then `tar' that subdirectory.
Compress the tar file with `gzip'. For example, the actual
distribution file for GCC version 1.40 is called `gcc-1.40.tar.gz'.
It is ok to support other free compression formats as well.
The `dist' target should explicitly depend on all non-source files
that are in the distribution, to make sure they are up to date in
the distribution. *Note Making Releases: Releases.
`check'
Perform self-tests (if any). The user must build the program
before running the tests, but need not install the program; you
should write the self-tests so that they work when the program is
built but not installed.
The following targets are suggested as conventional names, for
programs in which they are useful.
`installcheck'
Perform installation tests (if any). The user must build and
install the program before running the tests. You should not
assume that `$(bindir)' is in the search path.
`installdirs'
It's useful to add a target named `installdirs' to create the
directories where files are installed, and their parent
directories. There is a script called `mkinstalldirs' which is
convenient for this; you can find it in the Gnulib package. You
can use a rule like this:
# Make sure all installation directories (e.g. $(bindir))
# actually exist by making them if necessary.
installdirs: mkinstalldirs
$(srcdir)/mkinstalldirs $(bindir) $(datadir) \
$(libdir) $(infodir) \
$(mandir)
or, if you wish to support `DESTDIR' (strongly encouraged),
# Make sure all installation directories (e.g. $(bindir))
# actually exist by making them if necessary.
installdirs: mkinstalldirs
$(srcdir)/mkinstalldirs \
$(DESTDIR)$(bindir) $(DESTDIR)$(datadir) \
$(DESTDIR)$(libdir) $(DESTDIR)$(infodir) \
$(DESTDIR)$(mandir)
This rule should not modify the directories where compilation is
done. It should do nothing but create installation directories.
File: standards.info, Node: Install Command Categories, Prev: Standard Targets, Up: Makefile Conventions
7.2.7 Install Command Categories
--------------------------------
When writing the `install' target, you must classify all the commands
into three categories: normal ones, "pre-installation" commands and
"post-installation" commands.
Normal commands move files into their proper places, and set their
modes. They may not alter any files except the ones that come entirely
from the package they belong to.
Pre-installation and post-installation commands may alter other
files; in particular, they can edit global configuration files or data
bases.
Pre-installation commands are typically executed before the normal
commands, and post-installation commands are typically run after the
normal commands.
The most common use for a post-installation command is to run
`install-info'. This cannot be done with a normal command, since it
alters a file (the Info directory) which does not come entirely and
solely from the package being installed. It is a post-installation
command because it needs to be done after the normal command which
installs the package's Info files.
Most programs don't need any pre-installation commands, but we have
the feature just in case it is needed.
To classify the commands in the `install' rule into these three
categories, insert "category lines" among them. A category line
specifies the category for the commands that follow.
A category line consists of a tab and a reference to a special Make
variable, plus an optional comment at the end. There are three
variables you can use, one for each category; the variable name
specifies the category. Category lines are no-ops in ordinary execution
because these three Make variables are normally undefined (and you
_should not_ define them in the makefile).
Here are the three possible category lines, each with a comment that
explains what it means:
$(PRE_INSTALL) # Pre-install commands follow.
$(POST_INSTALL) # Post-install commands follow.
$(NORMAL_INSTALL) # Normal commands follow.
If you don't use a category line at the beginning of the `install'
rule, all the commands are classified as normal until the first category
line. If you don't use any category lines, all the commands are
classified as normal.
These are the category lines for `uninstall':
$(PRE_UNINSTALL) # Pre-uninstall commands follow.
$(POST_UNINSTALL) # Post-uninstall commands follow.
$(NORMAL_UNINSTALL) # Normal commands follow.
Typically, a pre-uninstall command would be used for deleting entries
from the Info directory.
If the `install' or `uninstall' target has any dependencies which
act as subroutines of installation, then you should start _each_
dependency's commands with a category line, and start the main target's
commands with a category line also. This way, you can ensure that each
command is placed in the right category regardless of which of the
dependencies actually run.
Pre-installation and post-installation commands should not run any
programs except for these:
[ basename bash cat chgrp chmod chown cmp cp dd diff echo
egrep expand expr false fgrep find getopt grep gunzip gzip
hostname install install-info kill ldconfig ln ls md5sum
mkdir mkfifo mknod mv printenv pwd rm rmdir sed sort tee
test touch true uname xargs yes
The reason for distinguishing the commands in this way is for the
sake of making binary packages. Typically a binary package contains
all the executables and other files that need to be installed, and has
its own method of installing them--so it does not need to run the normal
installation commands. But installing the binary package does need to
execute the pre-installation and post-installation commands.
Programs to build binary packages work by extracting the
pre-installation and post-installation commands. Here is one way of
extracting the pre-installation commands (the `-s' option to `make' is
needed to silence messages about entering subdirectories):
make -s -n install -o all \
PRE_INSTALL=pre-install \
POST_INSTALL=post-install \
NORMAL_INSTALL=normal-install \
| gawk -f pre-install.awk
where the file `pre-install.awk' could contain this:
$0 ~ /^(normal-install|post-install)[ \t]*$/ {on = 0}
on {print $0}
$0 ~ /^pre-install[ \t]*$/ {on = 1}
File: standards.info, Node: Releases, Prev: Makefile Conventions, Up: Managing Releases
7.3 Making Releases
===================
You should identify each release with a pair of version numbers, a
major version and a minor. We have no objection to using more than two
numbers, but it is very unlikely that you really need them.
Package the distribution of `Foo version 69.96' up in a gzipped tar
file with the name `foo-69.96.tar.gz'. It should unpack into a
subdirectory named `foo-69.96'.
Building and installing the program should never modify any of the
files contained in the distribution. This means that all the files
that form part of the program in any way must be classified into "source
files" and "non-source files". Source files are written by humans and
never changed automatically; non-source files are produced from source
files by programs under the control of the Makefile.
The distribution should contain a file named `README' which gives
the name of the package, and a general description of what it does. It
is also good to explain the purpose of each of the first-level
subdirectories in the package, if there are any. The `README' file
should either state the version number of the package, or refer to where
in the package it can be found.
The `README' file should refer to the file `INSTALL', which should
contain an explanation of the installation procedure.
The `README' file should also refer to the file which contains the
copying conditions. The GNU GPL, if used, should be in a file called
`COPYING'. If the GNU LGPL is used, it should be in a file called
`COPYING.LESSER'.
Naturally, all the source files must be in the distribution. It is
okay to include non-source files in the distribution along with the
source files they are generated from, provided they are up-to-date with
the source they are made from, and machine-independent, so that normal
building of the distribution will never modify them. We commonly
include non-source files produced by Autoconf, Automake, Bison, `lex',
TeX, and `makeinfo'; this helps avoid unnecessary dependencies between
our distributions, so that users can install whichever packages they
want to install.
Non-source files that might actually be modified by building and
installing the program should *never* be included in the distribution.
So if you do distribute non-source files, always make sure they are up
to date when you make a new distribution.
Make sure that all the files in the distribution are world-readable,
and that directories are world-readable and world-searchable (octal
mode 755). We used to recommend that all directories in the
distribution also be world-writable (octal mode 777), because ancient
versions of `tar' would otherwise not cope when extracting the archive
as an unprivileged user. That can easily lead to security issues when
creating the archive, however, so now we recommend against that.
Don't include any symbolic links in the distribution itself. If the
tar file contains symbolic links, then people cannot even unpack it on
systems that don't support symbolic links. Also, don't use multiple
names for one file in different directories, because certain file
systems cannot handle this and that prevents unpacking the distribution.
Try to make sure that all the file names will be unique on MS-DOS. A
name on MS-DOS consists of up to 8 characters, optionally followed by a
period and up to three characters. MS-DOS will truncate extra
characters both before and after the period. Thus, `foobarhacker.c'
and `foobarhacker.o' are not ambiguous; they are truncated to
`foobarha.c' and `foobarha.o', which are distinct.
Include in your distribution a copy of the `texinfo.tex' you used to
test print any `*.texinfo' or `*.texi' files.
Likewise, if your program uses small GNU software packages like
regex, getopt, obstack, or termcap, include them in the distribution
file. Leaving them out would make the distribution file a little
smaller at the expense of possible inconvenience to a user who doesn't
know what other files to get.
File: standards.info, Node: References, Next: GNU Free Documentation License, Prev: Managing Releases, Up: Top
8 References to Non-Free Software and Documentation
***************************************************
A GNU program should not recommend, promote, or grant legitimacy to the
use of any non-free program. Proprietary software is a social and
ethical problem, and our aim is to put an end to that problem. We
can't stop some people from writing proprietary programs, or stop other
people from using them, but we can and should refuse to advertise them
to new potential customers, or to give the public the idea that their
existence is ethical.
The GNU definition of free software is found on the GNU web site at
`http://www.gnu.org/philosophy/free-sw.html', and the definition of
free documentation is found at
`http://www.gnu.org/philosophy/free-doc.html'. The terms "free" and
"non-free", used in this document, refer to those definitions.
A list of important licenses and whether they qualify as free is in
`http://www.gnu.org/licenses/license-list.html'. If it is not clear
whether a license qualifies as free, please ask the GNU Project by
writing to . We will answer, and if the license is
an important one, we will add it to the list.
When a non-free program or system is well known, you can mention it
in passing--that is harmless, since users who might want to use it
probably already know about it. For instance, it is fine to explain
how to build your package on top of some widely used non-free operating
system, or how to use it together with some widely used non-free
program.
However, you should give only the necessary information to help those
who already use the non-free program to use your program with it--don't
give, or refer to, any further information about the proprietary
program, and don't imply that the proprietary program enhances your
program, or that its existence is in any way a good thing. The goal
should be that people already using the proprietary program will get
the advice they need about how to use your free program with it, while
people who don't already use the proprietary program will not see
anything likely to lead them to take an interest in it.
If a non-free program or system is obscure in your program's domain,
your program should not mention or support it at all, since doing so
would tend to popularize the non-free program more than it popularizes
your program. (You cannot hope to find many additional users for your
program among the users of Foobar, if the existence of Foobar is not
generally known among people who might want to use your program.)
Sometimes a program is free software in itself but depends on a
non-free platform in order to run. For instance, many Java programs
depend on some non-free Java libraries. To recommend or promote such a
program is to promote the other programs it needs. This is why we are
careful about listing Java programs in the Free Software Directory: we
don't want to promote the non-free Java libraries.
We hope this particular problem with Java will be gone by and by, as
we replace the remaining non-free standard Java libraries with free
software, but the general principle will remain the same: don't
recommend, promote or legitimize programs that depend on non-free
software to run.
Some free programs strongly encourage the use of non-free software.
A typical example is `mplayer'. It is free software in itself, and the
free code can handle some kinds of files. However, `mplayer'
recommends use of non-free codecs for other kinds of files, and users
that install `mplayer' are very likely to install those codecs along
with it. To recommend `mplayer' is, in effect, to promote use of the
non-free codecs.
Thus, you should not recommend programs that strongly encourage the
use of non-free software. This is why we do not list `mplayer' in the
Free Software Directory.
A GNU package should not refer the user to any non-free documentation
for free software. Free documentation that can be included in free
operating systems is essential for completing the GNU system, or any
free operating system, so encouraging it is a priority; to recommend
use of documentation that we are not allowed to include undermines the
impetus for the community to produce documentation that we can include.
So GNU packages should never recommend non-free documentation.
By contrast, it is ok to refer to journal articles and textbooks in
the comments of a program for explanation of how it functions, even
though they are non-free. This is because we don't include such things
in the GNU system even if they are free--they are outside the scope of
what a software distribution needs to include.
Referring to a web site that describes or recommends a non-free
program is promoting that program, so please do not make links to (or
mention by name) web sites that contain such material. This policy is
relevant particularly for the web pages for a GNU package.
Following links from nearly any web site can lead eventually to
non-free software; this is inherent in the nature of the web. So it
makes no sense to criticize a site for having such links. As long as
the site does not itself recommend a non-free program, there is no need
to consider the question of the sites that it links to for other
reasons.
Thus, for example, you should not refer to AT&T's web site if that
recommends AT&T's non-free software packages; you should not refer to a
site that links to AT&T's site presenting it as a place to get some
non-free program, because that link recommends and legitimizes the
non-free program. However, that a site contains a link to AT&T's web
site for some other purpose (such as long-distance telephone service)
is not an objection against it.
File: standards.info, Node: GNU Free Documentation License, Next: Index, Prev: References, Up: Top
Appendix A GNU Free Documentation License
*****************************************
Version 1.3, 3 November 2008
Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
`http://fsf.org/'
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or
noncommercially. Secondarily, this License preserves for the
author and publisher a way to get credit for their work, while not
being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.
It complements the GNU General Public License, which is a copyleft
license designed for free software.
We have designed this License in order to use it for manuals for
free software, because free software needs free documentation: a
free program should come with manuals providing the same freedoms
that the software does. But this License is not limited to
software manuals; it can be used for any textual work, regardless
of subject matter or whether it is published as a printed book.
We recommend this License principally for works whose purpose is
instruction or reference.
1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium,
that contains a notice placed by the copyright holder saying it
can be distributed under the terms of this License. Such a notice
grants a world-wide, royalty-free license, unlimited in duration,
to use that work under the conditions stated herein. The
"Document", below, refers to any such manual or work. Any member
of the public is a licensee, and is addressed as "you". You
accept the license if you copy, modify or distribute the work in a
way requiring permission under copyright law.
A "Modified Version" of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.
A "Secondary Section" is a named appendix or a front-matter section
of the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document's overall
subject (or to related matters) and contains nothing that could
fall directly within that overall subject. (Thus, if the Document
is in part a textbook of mathematics, a Secondary Section may not
explain any mathematics.) The relationship could be a matter of
historical connection with the subject or with related matters, or
of legal, commercial, philosophical, ethical or political position
regarding them.
The "Invariant Sections" are certain Secondary Sections whose
titles are designated, as being those of Invariant Sections, in
the notice that says that the Document is released under this
License. If a section does not fit the above definition of
Secondary then it is not allowed to be designated as Invariant.
The Document may contain zero Invariant Sections. If the Document
does not identify any Invariant Sections then there are none.
The "Cover Texts" are certain short passages of text that are
listed, as Front-Cover Texts or Back-Cover Texts, in the notice
that says that the Document is released under this License. A
Front-Cover Text may be at most 5 words, and a Back-Cover Text may
be at most 25 words.
A "Transparent" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
general public, that is suitable for revising the document
straightforwardly with generic text editors or (for images
composed of pixels) generic paint programs or (for drawings) some
widely available drawing editor, and that is suitable for input to
text formatters or for automatic translation to a variety of
formats suitable for input to text formatters. A copy made in an
otherwise Transparent file format whose markup, or absence of
markup, has been arranged to thwart or discourage subsequent
modification by readers is not Transparent. An image format is
not Transparent if used for any substantial amount of text. A
copy that is not "Transparent" is called "Opaque".
Examples of suitable formats for Transparent copies include plain
ASCII without markup, Texinfo input format, LaTeX input format,
SGML or XML using a publicly available DTD, and
standard-conforming simple HTML, PostScript or PDF designed for
human modification. Examples of transparent image formats include
PNG, XCF and JPG. Opaque formats include proprietary formats that
can be read and edited only by proprietary word processors, SGML or
XML for which the DTD and/or processing tools are not generally
available, and the machine-generated HTML, PostScript or PDF
produced by some word processors for output purposes only.
The "Title Page" means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the
material this License requires to appear in the title page. For
works in formats which do not have any title page as such, "Title
Page" means the text near the most prominent appearance of the
work's title, preceding the beginning of the body of the text.
The "publisher" means any person or entity that distributes copies
of the Document to the public.
A section "Entitled XYZ" means a named subunit of the Document
whose title either is precisely XYZ or contains XYZ in parentheses
following text that translates XYZ in another language. (Here XYZ
stands for a specific section name mentioned below, such as
"Acknowledgements", "Dedications", "Endorsements", or "History".)
To "Preserve the Title" of such a section when you modify the
Document means that it remains a section "Entitled XYZ" according
to this definition.
The Document may include Warranty Disclaimers next to the notice
which states that this License applies to the Document. These
Warranty Disclaimers are considered to be included by reference in
this License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and
has no effect on the meaning of this License.
2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License
applies to the Document are reproduced in all copies, and that you
add no other conditions whatsoever to those of this License. You
may not use technical measures to obstruct or control the reading
or further copying of the copies you make or distribute. However,
you may accept compensation in exchange for copies. If you
distribute a large enough number of copies you must also follow
the conditions in section 3.
You may also lend copies, under the same conditions stated above,
and you may publicly display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly
have printed covers) of the Document, numbering more than 100, and
the Document's license notice requires Cover Texts, you must
enclose the copies in covers that carry, clearly and legibly, all
these Cover Texts: Front-Cover Texts on the front cover, and
Back-Cover Texts on the back cover. Both covers must also clearly
and legibly identify you as the publisher of these copies. The
front cover must present the full title with all words of the
title equally prominent and visible. You may add other material
on the covers in addition. Copying with changes limited to the
covers, as long as they preserve the title of the Document and
satisfy these conditions, can be treated as verbatim copying in
other respects.
If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto
adjacent pages.
If you publish or distribute Opaque copies of the Document
numbering more than 100, you must either include a
machine-readable Transparent copy along with each Opaque copy, or
state in or with each Opaque copy a computer-network location from
which the general network-using public has access to download
using public-standard network protocols a complete Transparent
copy of the Document, free of added material. If you use the
latter option, you must take reasonably prudent steps, when you
begin distribution of Opaque copies in quantity, to ensure that
this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you
distribute an Opaque copy (directly or through your agents or
retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of
the Document well before redistributing any large number of
copies, to give them a chance to provide you with an updated
version of the Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document
under the conditions of sections 2 and 3 above, provided that you
release the Modified Version under precisely this License, with
the Modified Version filling the role of the Document, thus
licensing distribution and modification of the Modified Version to
whoever possesses a copy of it. In addition, you must do these
things in the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title
distinct from that of the Document, and from those of
previous versions (which should, if there were any, be listed
in the History section of the Document). You may use the
same title as a previous version if the original publisher of
that version gives permission.
B. List on the Title Page, as authors, one or more persons or
entities responsible for authorship of the modifications in
the Modified Version, together with at least five of the
principal authors of the Document (all of its principal
authors, if it has fewer than five), unless they release you
from this requirement.
C. State on the Title page the name of the publisher of the
Modified Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license
notice giving the public permission to use the Modified
Version under the terms of this License, in the form shown in
the Addendum below.
G. Preserve in that license notice the full lists of Invariant
Sections and required Cover Texts given in the Document's
license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled "History", Preserve its Title,
and add to it an item stating at least the title, year, new
authors, and publisher of the Modified Version as given on
the Title Page. If there is no section Entitled "History" in
the Document, create one stating the title, year, authors,
and publisher of the Document as given on its Title Page,
then add an item describing the Modified Version as stated in
the previous sentence.
J. Preserve the network location, if any, given in the Document
for public access to a Transparent copy of the Document, and
likewise the network locations given in the Document for
previous versions it was based on. These may be placed in
the "History" section. You may omit a network location for a
work that was published at least four years before the
Document itself, or if the original publisher of the version
it refers to gives permission.
K. For any section Entitled "Acknowledgements" or "Dedications",
Preserve the Title of the section, and preserve in the
section all the substance and tone of each of the contributor
acknowledgements and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles. Section numbers
or the equivalent are not considered part of the section
titles.
M. Delete any section Entitled "Endorsements". Such a section
may not be included in the Modified Version.
N. Do not retitle any existing section to be Entitled
"Endorsements" or to conflict in title with any Invariant
Section.
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no
material copied from the Document, you may at your option
designate some or all of these sections as invariant. To do this,
add their titles to the list of Invariant Sections in the Modified
Version's license notice. These titles must be distinct from any
other section titles.
You may add a section Entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
parties--for example, statements of peer review or that the text
has been approved by an organization as the authoritative
definition of a standard.
You may add a passage of up to five words as a Front-Cover Text,
and a passage of up to 25 words as a Back-Cover Text, to the end
of the list of Cover Texts in the Modified Version. Only one
passage of Front-Cover Text and one of Back-Cover Text may be
added by (or through arrangements made by) any one entity. If the
Document already includes a cover text for the same cover,
previously added by you or by arrangement made by the same entity
you are acting on behalf of, you may not add another; but you may
replace the old one, on explicit permission from the previous
publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this
License give permission to use their names for publicity for or to
assert or imply endorsement of any Modified Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under
this License, under the terms defined in section 4 above for
modified versions, provided that you include in the combination
all of the Invariant Sections of all of the original documents,
unmodified, and list them all as Invariant Sections of your
combined work in its license notice, and that you preserve all
their Warranty Disclaimers.
The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy. If there are multiple Invariant Sections with the same name
but different contents, make the title of each such section unique
by adding at the end of it, in parentheses, the name of the
original author or publisher of that section if known, or else a
unique number. Make the same adjustment to the section titles in
the list of Invariant Sections in the license notice of the
combined work.
In the combination, you must combine any sections Entitled
"History" in the various original documents, forming one section
Entitled "History"; likewise combine any sections Entitled
"Acknowledgements", and any sections Entitled "Dedications". You
must delete all sections Entitled "Endorsements."
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other
documents released under this License, and replace the individual
copies of this License in the various documents with a single copy
that is included in the collection, provided that you follow the
rules of this License for verbatim copying of each of the
documents in all other respects.
You may extract a single document from such a collection, and
distribute it individually under this License, provided you insert
a copy of this License into the extracted document, and follow
this License in all other respects regarding verbatim copying of
that document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other
separate and independent documents or works, in or on a volume of
a storage or distribution medium, is called an "aggregate" if the
copyright resulting from the compilation is not used to limit the
legal rights of the compilation's users beyond what the individual
works permit. When the Document is included in an aggregate, this
License does not apply to the other works in the aggregate which
are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half
of the entire aggregate, the Document's Cover Texts may be placed
on covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic
form. Otherwise they must appear on printed covers that bracket
the whole aggregate.
8. TRANSLATION
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section
4. Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also
include the original English version of this License and the
original versions of those notices and disclaimers. In case of a
disagreement between the translation and the original version of
this License or a notice or disclaimer, the original version will
prevail.
If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to
Preserve its Title (section 1) will typically require changing the
actual title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document
except as expressly provided under this License. Any attempt
otherwise to copy, modify, sublicense, or distribute it is void,
and will automatically terminate your rights under this License.
However, if you cease all violation of this License, then your
license from a particular copyright holder is reinstated (a)
provisionally, unless and until the copyright holder explicitly
and finally terminates your license, and (b) permanently, if the
copyright holder fails to notify you of the violation by some
reasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is
reinstated permanently if the copyright holder notifies you of the
violation by some reasonable means, this is the first time you have
received notice of violation of this License (for any work) from
that copyright holder, and you cure the violation prior to 30 days
after your receipt of the notice.
Termination of your rights under this section does not terminate
the licenses of parties who have received copies or rights from
you under this License. If your rights have been terminated and
not permanently reinstated, receipt of a copy of some or all of
the same material does not give you any rights to use it.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of
the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
`http://www.gnu.org/copyleft/'.
Each version of the License is given a distinguishing version
number. If the Document specifies that a particular numbered
version of this License "or any later version" applies to it, you
have the option of following the terms and conditions either of
that specified version or of any later version that has been
published (not as a draft) by the Free Software Foundation. If
the Document does not specify a version number of this License,
you may choose any version ever published (not as a draft) by the
Free Software Foundation. If the Document specifies that a proxy
can decide which future versions of this License can be used, that
proxy's public statement of acceptance of a version permanently
authorizes you to choose that version for the Document.
11. RELICENSING
"Massive Multiauthor Collaboration Site" (or "MMC Site") means any
World Wide Web server that publishes copyrightable works and also
provides prominent facilities for anybody to edit those works. A
public wiki that anybody can edit is an example of such a server.
A "Massive Multiauthor Collaboration" (or "MMC") contained in the
site means any set of copyrightable works thus published on the MMC
site.
"CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
license published by Creative Commons Corporation, a not-for-profit
corporation with a principal place of business in San Francisco,
California, as well as future copyleft versions of that license
published by that same organization.
"Incorporate" means to publish or republish a Document, in whole or
in part, as part of another Document.
An MMC is "eligible for relicensing" if it is licensed under this
License, and if all works that were first published under this
License somewhere other than this MMC, and subsequently
incorporated in whole or in part into the MMC, (1) had no cover
texts or invariant sections, and (2) were thus incorporated prior
to November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the
site under CC-BY-SA on the same site at any time before August 1,
2009, provided the MMC is eligible for relicensing.
ADDENDUM: How to use this License for your documents
====================================================
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:
Copyright (C) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts. A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:
with the Invariant Sections being LIST THEIR TITLES, with
the Front-Cover Texts being LIST, and with the Back-Cover Texts
being LIST.
If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.
If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.
File: standards.info, Node: Index, Prev: GNU Free Documentation License, Up: Top
Index
*****
[index ]
* Menu:
* #endif, commenting: Comments. (line 60)
* --help output: --help. (line 6)
* --version output: --version. (line 6)
* -Wall compiler option: Syntactic Conventions.
(line 10)
* accepting contributions: Contributions. (line 6)
* address for bug reports: --help. (line 11)
* ANSI C standard: Standard C. (line 6)
* arbitrary limits on data: Semantics. (line 6)
* ASCII characters: Character Set. (line 6)
* autoconf: System Portability. (line 23)
* avoiding proprietary code: Reading Non-Free Code.
(line 6)
* behavior, dependent on program's name: User Interfaces. (line 6)
* binary packages: Install Command Categories.
(line 80)
* bindir: Directory Variables. (line 57)
* braces, in C source: Formatting. (line 6)
* bug reports: --help. (line 11)
* bug-standards@gnu.org email address: Preface. (line 30)
* C library functions, and portability: System Functions. (line 6)
* canonical name of a program: --version. (line 12)
* casting pointers to integers: CPU Portability. (line 50)
* CGI programs, standard options for: Command-Line Interfaces.
(line 31)
* change logs: Change Logs. (line 6)
* change logs, conditional changes: Conditional Changes. (line 6)
* change logs, style: Style of Change Logs.
(line 6)
* character set: Character Set. (line 6)
* clang: Syntactic Conventions.
(line 17)
* command-line arguments, decoding: Semantics. (line 47)
* command-line interface: Command-Line Interfaces.
(line 6)
* commenting: Comments. (line 6)
* compatibility with C and POSIX standards: Compatibility. (line 6)
* compiler warnings: Syntactic Conventions.
(line 10)
* conditional changes, and change logs: Conditional Changes. (line 6)
* conditionals, comments for: Comments. (line 60)
* configure: Configuration. (line 6)
* control-L: Formatting. (line 128)
* conventions for makefiles: Makefile Conventions.
(line 6)
* CORBA: Graphical Interfaces.
(line 16)
* credits for manuals: Manual Credits. (line 6)
* D-bus: Graphical Interfaces.
(line 16)
* data structures, in Gnulib: System Functions. (line 44)
* data types, and portability: CPU Portability. (line 6)
* DESTDIR: DESTDIR. (line 6)
* directories, creating installation: Directory Variables. (line 20)
* documentation: Documentation. (line 6)
* doschk: Names. (line 38)
* double quote: Quote Characters. (line 6)
* downloading this manual: Preface. (line 14)
* dynamic plug-ins: Dynamic Plug-In Interfaces.
(line 6)
* encodings: Character Set. (line 6)
* enum types, formatting: Formatting. (line 45)
* error messages: Semantics. (line 19)
* error messages, formatting: Errors. (line 6)
* error messages, in Gnulib: System Functions. (line 44)
* exec_prefix: Directory Variables. (line 39)
* expressions, splitting: Formatting. (line 91)
* FDL, GNU Free Documentation License: GNU Free Documentation License.
(line 6)
* file usage: File Usage. (line 6)
* file-name limitations: Names. (line 38)
* formatting error messages: Errors. (line 6)
* formatting source code: Formatting. (line 6)
* formfeed: Formatting. (line 128)
* function argument, declaring: Syntactic Conventions.
(line 6)
* function definitions, formatting: Formatting. (line 6)
* function prototypes: Standard C. (line 17)
* getopt: Command-Line Interfaces.
(line 6)
* gettext: Internationalization.
(line 6)
* GNOME: Graphical Interfaces.
(line 16)
* GNOME and Guile: Source Language. (line 38)
* Gnulib: System Functions. (line 37)
* gnustandards project repository: Preface. (line 30)
* gnustandards-commit@gnu.org mailing list: Preface. (line 24)
* graphical user interface: Graphical Interfaces.
(line 6)
* grave accent: Quote Characters. (line 6)
* GTK+: Graphical Interfaces.
(line 6)
* Guile: Source Language. (line 38)
* implicit int: Syntactic Conventions.
(line 6)
* impossible conditions: Semantics. (line 71)
* installation directories, creating: Directory Variables. (line 20)
* installations, staged: DESTDIR. (line 6)
* interface styles: Graphical Interfaces.
(line 6)
* internationalization: Internationalization.
(line 6)
* keyboard interface: Graphical Interfaces.
(line 16)
* LDAP: OID Allocations. (line 6)
* left quote: Quote Characters. (line 6)
* legal aspects: Legal Issues. (line 6)
* legal papers: Contributions. (line 6)
* libexecdir: Directory Variables. (line 70)
* libiconv: Semantics. (line 11)
* libraries: Libraries. (line 6)
* library functions, and portability: System Functions. (line 6)
* library interface: Graphical Interfaces.
(line 16)
* license for manuals: License for Manuals. (line 6)
* lint: Syntactic Conventions.
(line 17)
* locale-specific quote characters: Quote Characters. (line 6)
* long option names: Option Table. (line 6)
* long-named options: Command-Line Interfaces.
(line 12)
* makefile, conventions for: Makefile Conventions.
(line 6)
* malloc return value: Semantics. (line 26)
* man pages: Man Pages. (line 6)
* manual structure: Manual Structure Details.
(line 6)
* memory allocation failure: Semantics. (line 26)
* memory leak: Memory Usage. (line 23)
* memory usage: Memory Usage. (line 6)
* message text, and internationalization: Internationalization.
(line 29)
* mmap: Mmap. (line 6)
* multiple variables in a line: Syntactic Conventions.
(line 43)
* names of variables, functions, and files: Names. (line 6)
* NEWS file: NEWS File. (line 6)
* non-ASCII characters: Character Set. (line 6)
* non-POSIX systems, and portability: System Portability. (line 32)
* non-standard extensions: Using Extensions. (line 6)
* NUL characters: Semantics. (line 11)
* OID allocations for GNU: OID Allocations. (line 6)
* open brace: Formatting. (line 6)
* opening quote: Quote Characters. (line 6)
* optional features, configure-time: Configuration. (line 100)
* options for compatibility: Compatibility. (line 14)
* options, standard command-line: Command-Line Interfaces.
(line 31)
* output device and program's behavior: User Interfaces. (line 13)
* packaging: Releases. (line 6)
* PATH_INFO, specifying standard options as: Command-Line Interfaces.
(line 31)
* plug-ins: Dynamic Plug-In Interfaces.
(line 6)
* plugin_is_GPL_compatible: Dynamic Plug-In Interfaces.
(line 17)
* portability, and data types: CPU Portability. (line 6)
* portability, and library functions: System Functions. (line 6)
* portability, between system types: System Portability. (line 6)
* POSIX compatibility: Compatibility. (line 6)
* POSIX functions, and portability: System Functions. (line 6)
* POSIXLY_CORRECT, environment variable: Compatibility. (line 21)
* post-installation commands: Install Command Categories.
(line 6)
* pre-installation commands: Install Command Categories.
(line 6)
* prefix: Directory Variables. (line 29)
* program configuration: Configuration. (line 6)
* program design: Design Advice. (line 6)
* program name and its behavior: User Interfaces. (line 6)
* program's canonical name: --version. (line 12)
* programming languages: Source Language. (line 6)
* proprietary programs: Reading Non-Free Code.
(line 6)
* quote characters: Quote Characters. (line 6)
* README file: Releases. (line 21)
* references to non-free material: References. (line 6)
* releasing: Managing Releases. (line 6)
* right quote: Quote Characters. (line 6)
* Savannah repository for gnustandards: Preface. (line 30)
* sbindir: Directory Variables. (line 63)
* signal handling: Semantics. (line 60)
* single quote: Quote Characters. (line 6)
* SNMP: OID Allocations. (line 6)
* spaces before open-paren: Formatting. (line 85)
* staged installs: DESTDIR. (line 6)
* standard command-line options: Command-Line Interfaces.
(line 31)
* standards for makefiles: Makefile Conventions.
(line 6)
* struct types, formatting: Formatting. (line 45)
* syntactic conventions: Syntactic Conventions.
(line 6)
* table of long options: Option Table. (line 6)
* temporary files: Semantics. (line 85)
* temporary variables: Syntactic Conventions.
(line 31)
* texinfo.tex, in a distribution: Releases. (line 72)
* TMPDIR environment variable: Semantics. (line 85)
* trademarks: Trademarks. (line 6)
* user interface styles: Graphical Interfaces.
(line 6)
* valgrind: Memory Usage. (line 23)
* where to obtain standards.texi: Preface. (line 14)
* X.509: OID Allocations. (line 6)
* xmalloc, in Gnulib: System Functions. (line 44)
Tag Table:
Node: Top824
Node: Preface2122
Node: Legal Issues4834
Node: Reading Non-Free Code5304
Node: Contributions7034
Node: Trademarks9220
Node: Design Advice10855
Node: Source Language11447
Node: Compatibility13573
Node: Using Extensions15201
Node: Standard C16777
Node: Conditional Compilation19180
Node: Program Behavior20578
Node: Non-GNU Standards21768
Node: Semantics24049
Node: Libraries28993
Node: Errors30238
Node: User Interfaces32807
Node: Graphical Interfaces34412
Node: Command-Line Interfaces35596
Node: --version37642
Node: --help43380
Node: Dynamic Plug-In Interfaces44253
Node: Option Table46152
Node: OID Allocations61110
Node: Memory Usage62944
Node: File Usage64219
Node: Writing C64969
Node: Formatting65950
Node: Comments70438
Node: Syntactic Conventions73990
Node: Names77965
Node: System Portability80177
Node: CPU Portability83068
Node: System Functions85434
Node: Internationalization87976
Node: Character Set91976
Node: Quote Characters92831
Node: Mmap94390
Node: Documentation95098
Node: GNU Manuals96204
Node: Doc Strings and Manuals101942
Node: Manual Structure Details103495
Node: License for Manuals104913
Node: Manual Credits105887
Node: Printed Manuals106280
Node: NEWS File106966
Node: Change Logs107644
Node: Change Log Concepts108398
Node: Style of Change Logs110501
Node: Simple Changes113001
Node: Conditional Changes114443
Node: Indicating the Part Changed116884
Node: Man Pages117411
Node: Reading other Manuals119617
Node: Managing Releases120408
Node: Configuration121189
Node: Makefile Conventions129854
Node: Makefile Basics130853
Node: Utilities in Makefiles134027
Node: Command Variables136532
Node: DESTDIR139778
Node: Directory Variables141952
Node: Standard Targets156574
Node: Install Command Categories170675
Node: Releases175208
Node: References179322
Node: GNU Free Documentation License185175
Node: Index210342
End Tag Table
0707010000cb81000081a400000000000000000000000153156594000017110000011f00010018ffffffffffffffff0000001e00000000root/usr/local/share/info/dir This is the file .../info/dir, which contains the
topmost node of the Info hierarchy, called (dir)Top.
The first time you invoke Info you start off looking at this node.
File: dir, Node: Top This is the top of the INFO tree
This (the Directory node) gives a menu of major topics.
Typing "q" exits, "?" lists all Info commands, "d" returns here,
"h" gives a primer for first-timers,
"mEmacs" visits the Emacs manual, etc.
In Emacs, you can click mouse button 2 on a menu item or cross reference
to select it.
* Menu:
GNU organization
* Standards: (standards). GNU coding standards.
Libraries
* History: (history). The GNU history library API.
* RLuserman: (rluserman). The GNU readline library User's Manual.
* Readline: (readline). The GNU readline library API.
C++ libraries
* autosprintf: (autosprintf). Support for printf format strings in C++.
GNU Gettext Utilities
* ISO3166: (gettext)Country Codes. ISO 3166 country codes.
* ISO639: (gettext)Language Codes. ISO 639 language codes.
* autopoint: (gettext)autopoint Invocation. Copy gettext infrastructure.
* envsubst: (gettext)envsubst Invocation. Expand environment variables.
* gettext: (gettext). GNU gettext utilities.
* gettextize: (gettext)gettextize Invocation. Prepare a package for gettext.
* msgattrib: (gettext)msgattrib Invocation. Select part of a PO file.
* msgcat: (gettext)msgcat Invocation. Combine several PO files.
* msgcmp: (gettext)msgcmp Invocation. Compare a PO file and template.
* msgcomm: (gettext)msgcomm Invocation. Match two PO files.
* msgconv: (gettext)msgconv Invocation. Convert PO file to encoding.
* msgen: (gettext)msgen Invocation. Create an English PO file.
* msgexec: (gettext)msgexec Invocation. Process a PO file.
* msgfilter: (gettext)msgfilter Invocation. Pipe a PO file through a filter.
* msgfmt: (gettext)msgfmt Invocation. Make MO files out of PO files.
* msggrep: (gettext)msggrep Invocation. Select part of a PO file.
* msginit: (gettext)msginit Invocation. Create a fresh PO file.
* msgmerge: (gettext)msgmerge Invocation. Update a PO file from template.
* msgunfmt: (gettext)msgunfmt Invocation. Uncompile MO file into PO file.
* msguniq: (gettext)msguniq Invocation. Unify duplicates for PO file.
* ngettext: (gettext)ngettext Invocation. Translate a message with plural.
* xgettext: (gettext)xgettext Invocation. Extract strings into a PO file.
Software development
* Autoconf: (autoconf). Create source code configuration scripts.
* GNU libunistring: (libunistring). Unicode string library.
* Make: (make). Remake files automatically.
* bison: (bison). GNU parser generator (Yacc replacement).
Basics
* Bash: (bash). The GNU Bourne-Again SHell.
Emacs
* IDN Library: (libidn)Emacs API. Emacs API for IDN functions.
Localization
* idn: (libidn)Invoking idn. Internationalized Domain Name (IDN) string conversion.
Software libraries
* libidn: (libidn). Internationalized string processing library.
Individual utilities
* autoconf-invocation: (autoconf)autoconf Invocation.
How to create configuration
scripts
* autoheader: (autoconf)autoheader Invocation. How to create configuration
templates
* autom4te: (autoconf)autom4te Invocation. The Autoconf executables
backbone
* autoreconf: (autoconf)autoreconf Invocation. Remaking multiple `configure'
scripts
* autoscan: (autoconf)autoscan Invocation. Semi-automatic `configure.ac'
writing
* autoupdate: (autoconf)autoupdate Invocation. Automatic update of
`configure.ac'
* awk: (gawk)Invoking gawk. Text scanning and processing.
* config.status: (autoconf)config.status Invocation.
Recreating configurations.
* configure: (autoconf)configure Invocation. Configuring a package.
* ifnames: (autoconf)ifnames Invocation. Listing conditionals in source.
* tar: (tar)tar invocation. Invoking GNU `tar'.
* testsuite: (autoconf)testsuite Invocation. Running an Autotest test suite.
Texinfo documentation system
* Info: (info). How to use the documentation browsing system.
* info stand-alone: (info-stnd).
Read Info documents without Emacs.
* infokey: (info-stnd)Invoking infokey.
Compile Info customizations.
* install-info: (texinfo)Invoking install-info.
Update info/dir entries.
* makeinfo: (texinfo)Invoking makeinfo.
Translate Texinfo source.
* pdftexi2dvi: (texinfo)PDF Output.
PDF output for Texinfo.
* pod2texi: (pod2texi)Invoking pod2texi.
Translate Perl POD to Texinfo.
* texi2dvi: (texinfo)Format with texi2dvi.
Print Texinfo documents.
* texi2pdf: (texinfo)PDF Output.
PDF output for Texinfo.
* texindex: (texinfo)Format with tex/texindex.
Sort Texinfo index files.
* Texinfo: (texinfo). The GNU documentation format.
Text creation and manipulation
* Gawk: (gawk). A text scanning and processing language.
Network applications
* Gawkinet: (gawkinet). TCP/IP Internetworking With `gawk'.
Archiving
* Tar: (tar). Making tape (or disk) archives.
0707010000cb80000081a40000000000000000000000015315659300116d1d0000011f00010018ffffffffffffffff0000002800000000root/usr/local/share/info/autoconf.info This is autoconf.info, produced by makeinfo version 4.13 from
autoconf.texi.
This manual (24 April 2012) is for GNU Autoconf (version 2.69), a
package for creating scripts to configure source code packages using
templates and an M4 macro package.
Copyright (C) 1992-1996, 1998-2012 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License,
Version 1.3 or any later version published by the Free Software
Foundation; with no Invariant Sections, no Front-Cover texts, and
no Back-Cover Texts. A copy of the license is included in the
section entitled "GNU Free Documentation License."
INFO-DIR-SECTION Software development
START-INFO-DIR-ENTRY
* Autoconf: (autoconf). Create source code configuration scripts.
END-INFO-DIR-ENTRY
INFO-DIR-SECTION Individual utilities
START-INFO-DIR-ENTRY
* autoscan: (autoconf)autoscan Invocation.
Semi-automatic `configure.ac' writing
* ifnames: (autoconf)ifnames Invocation. Listing conditionals in source.
* autoconf-invocation: (autoconf)autoconf Invocation.
How to create configuration scripts
* autoreconf: (autoconf)autoreconf Invocation.
Remaking multiple `configure' scripts
* autoheader: (autoconf)autoheader Invocation.
How to create configuration templates
* autom4te: (autoconf)autom4te Invocation.
The Autoconf executables backbone
* configure: (autoconf)configure Invocation. Configuring a package.
* autoupdate: (autoconf)autoupdate Invocation.
Automatic update of `configure.ac'
* config.status: (autoconf)config.status Invocation. Recreating configurations.
* testsuite: (autoconf)testsuite Invocation. Running an Autotest test suite.
END-INFO-DIR-ENTRY
File: autoconf.info, Node: Top, Next: Introduction, Up: (dir)
Autoconf
********
This manual (24 April 2012) is for GNU Autoconf (version 2.69), a
package for creating scripts to configure source code packages using
templates and an M4 macro package.
Copyright (C) 1992-1996, 1998-2012 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License,
Version 1.3 or any later version published by the Free Software
Foundation; with no Invariant Sections, no Front-Cover texts, and
no Back-Cover Texts. A copy of the license is included in the
section entitled "GNU Free Documentation License."
* Menu:
* Introduction:: Autoconf's purpose, strengths, and weaknesses
* The GNU Build System:: A set of tools for portable software packages
* Making configure Scripts:: How to organize and produce Autoconf scripts
* Setup:: Initialization and output
* Existing Tests:: Macros that check for particular features
* Writing Tests:: How to write new feature checks
* Results:: What to do with results from feature checks
* Programming in M4:: Layers on top of which Autoconf is written
* Programming in M4sh:: Shell portability layer
* Writing Autoconf Macros:: Adding new macros to Autoconf
* Portable Shell:: Shell script portability pitfalls
* Portable Make:: Makefile portability pitfalls
* Portable C and C++:: C and C++ portability pitfalls
* Manual Configuration:: Selecting features that can't be guessed
* Site Configuration:: Local defaults for `configure'
* Running configure Scripts:: How to use the Autoconf output
* config.status Invocation:: Recreating a configuration
* Obsolete Constructs:: Kept for backward compatibility
* Using Autotest:: Creating portable test suites
* FAQ:: Frequent Autoconf Questions, with answers
* History:: History of Autoconf
* GNU Free Documentation License:: License for copying this manual
* Indices:: Indices of symbols, concepts, etc.
--- The Detailed Node Listing ---
The GNU Build System
* Automake:: Escaping makefile hell
* Gnulib:: The GNU portability library
* Libtool:: Building libraries portably
* Pointers:: More info on the GNU build system
Making `configure' Scripts
* Writing Autoconf Input:: What to put in an Autoconf input file
* autoscan Invocation:: Semi-automatic `configure.ac' writing
* ifnames Invocation:: Listing the conditionals in source code
* autoconf Invocation:: How to create configuration scripts
* autoreconf Invocation:: Remaking multiple `configure' scripts
Writing `configure.ac'
* Shell Script Compiler:: Autoconf as solution of a problem
* Autoconf Language:: Programming in Autoconf
* Autoconf Input Layout:: Standard organization of `configure.ac'
Initialization and Output Files
* Initializing configure:: Option processing etc.
* Versioning:: Dealing with Autoconf versions
* Notices:: Copyright, version numbers in `configure'
* Input:: Where Autoconf should find files
* Output:: Outputting results from the configuration
* Configuration Actions:: Preparing the output based on results
* Configuration Files:: Creating output files
* Makefile Substitutions:: Using output variables in makefiles
* Configuration Headers:: Creating a configuration header file
* Configuration Commands:: Running arbitrary instantiation commands
* Configuration Links:: Links depending on the configuration
* Subdirectories:: Configuring independent packages together
* Default Prefix:: Changing the default installation prefix
Substitutions in Makefiles
* Preset Output Variables:: Output variables that are always set
* Installation Directory Variables:: Other preset output variables
* Changed Directory Variables:: Warnings about `datarootdir'
* Build Directories:: Supporting multiple concurrent compiles
* Automatic Remaking:: Makefile rules for configuring
Configuration Header Files
* Header Templates:: Input for the configuration headers
* autoheader Invocation:: How to create configuration templates
* Autoheader Macros:: How to specify CPP templates
Existing Tests
* Common Behavior:: Macros' standard schemes
* Alternative Programs:: Selecting between alternative programs
* Files:: Checking for the existence of files
* Libraries:: Library archives that might be missing
* Library Functions:: C library functions that might be missing
* Header Files:: Header files that might be missing
* Declarations:: Declarations that may be missing
* Structures:: Structures or members that might be missing
* Types:: Types that might be missing
* Compilers and Preprocessors:: Checking for compiling programs
* System Services:: Operating system services
* Posix Variants:: Special kludges for specific Posix variants
* Erlang Libraries:: Checking for the existence of Erlang libraries
Common Behavior
* Standard Symbols:: Symbols defined by the macros
* Default Includes:: Includes used by the generic macros
Alternative Programs
* Particular Programs:: Special handling to find certain programs
* Generic Programs:: How to find other programs
Library Functions
* Function Portability:: Pitfalls with usual functions
* Particular Functions:: Special handling to find certain functions
* Generic Functions:: How to find other functions
Header Files
* Header Portability:: Collected knowledge on common headers
* Particular Headers:: Special handling to find certain headers
* Generic Headers:: How to find other headers
Declarations
* Particular Declarations:: Macros to check for certain declarations
* Generic Declarations:: How to find other declarations
Structures
* Particular Structures:: Macros to check for certain structure members
* Generic Structures:: How to find other structure members
Types
* Particular Types:: Special handling to find certain types
* Generic Types:: How to find other types
Compilers and Preprocessors
* Specific Compiler Characteristics:: Some portability issues
* Generic Compiler Characteristics:: Language independent tests and features
* C Compiler:: Checking its characteristics
* C++ Compiler:: Likewise
* Objective C Compiler:: Likewise
* Objective C++ Compiler:: Likewise
* Erlang Compiler and Interpreter:: Likewise
* Fortran Compiler:: Likewise
* Go Compiler:: Likewise
Writing Tests
* Language Choice:: Selecting which language to use for testing
* Writing Test Programs:: Forging source files for compilers
* Running the Preprocessor:: Detecting preprocessor symbols
* Running the Compiler:: Detecting language or header features
* Running the Linker:: Detecting library features
* Runtime:: Testing for runtime features
* Systemology:: A zoology of operating systems
* Multiple Cases:: Tests for several possible values
Writing Test Programs
* Guidelines:: General rules for writing test programs
* Test Functions:: Avoiding pitfalls in test programs
* Generating Sources:: Source program boilerplate
Results of Tests
* Defining Symbols:: Defining C preprocessor symbols
* Setting Output Variables:: Replacing variables in output files
* Special Chars in Variables:: Characters to beware of in variables
* Caching Results:: Speeding up subsequent `configure' runs
* Printing Messages:: Notifying `configure' users
Caching Results
* Cache Variable Names:: Shell variables used in caches
* Cache Files:: Files `configure' uses for caching
* Cache Checkpointing:: Loading and saving the cache file
Programming in M4
* M4 Quotation:: Protecting macros from unwanted expansion
* Using autom4te:: The Autoconf executables backbone
* Programming in M4sugar:: Convenient pure M4 macros
* Debugging via autom4te:: Figuring out what M4 was doing
M4 Quotation
* Active Characters:: Characters that change the behavior of M4
* One Macro Call:: Quotation and one macro call
* Quoting and Parameters:: M4 vs. shell parameters
* Quotation and Nested Macros:: Macros calling macros
* Changequote is Evil:: Worse than INTERCAL: M4 + changequote
* Quadrigraphs:: Another way to escape special characters
* Balancing Parentheses:: Dealing with unbalanced parentheses
* Quotation Rule Of Thumb:: One parenthesis, one quote
Using `autom4te'
* autom4te Invocation:: A GNU M4 wrapper
* Customizing autom4te:: Customizing the Autoconf package
Programming in M4sugar
* Redefined M4 Macros:: M4 builtins changed in M4sugar
* Diagnostic Macros:: Diagnostic messages from M4sugar
* Diversion support:: Diversions in M4sugar
* Conditional constructs:: Conditions in M4
* Looping constructs:: Iteration in M4
* Evaluation Macros:: More quotation and evaluation control
* Text processing Macros:: String manipulation in M4
* Number processing Macros:: Arithmetic computation in M4
* Set manipulation Macros:: Set manipulation in M4
* Forbidden Patterns:: Catching unexpanded macros
Programming in M4sh
* Common Shell Constructs:: Portability layer for common shell constructs
* Polymorphic Variables:: Support for indirect variable names
* Initialization Macros:: Macros to establish a sane shell environment
* File Descriptor Macros:: File descriptor macros for input and output
Writing Autoconf Macros
* Macro Definitions:: Basic format of an Autoconf macro
* Macro Names:: What to call your new macros
* Reporting Messages:: Notifying `autoconf' users
* Dependencies Between Macros:: What to do when macros depend on other macros
* Obsoleting Macros:: Warning about old ways of doing things
* Coding Style:: Writing Autoconf macros a` la Autoconf
Dependencies Between Macros
* Prerequisite Macros:: Ensuring required information
* Suggested Ordering:: Warning about possible ordering problems
* One-Shot Macros:: Ensuring a macro is called only once
Portable Shell Programming
* Shellology:: A zoology of shells
* Invoking the Shell:: Invoking the shell as a command
* Here-Documents:: Quirks and tricks
* File Descriptors:: FDs and redirections
* Signal Handling:: Shells, signals, and headaches
* File System Conventions:: File names
* Shell Pattern Matching:: Pattern matching
* Shell Substitutions:: Variable and command expansions
* Assignments:: Varying side effects of assignments
* Parentheses:: Parentheses in shell scripts
* Slashes:: Slashes in shell scripts
* Special Shell Variables:: Variables you should not change
* Shell Functions:: What to look out for if you use them
* Limitations of Builtins:: Portable use of not so portable /bin/sh
* Limitations of Usual Tools:: Portable use of portable tools
Portable Make Programming
* $< in Ordinary Make Rules:: $< in ordinary rules
* Failure in Make Rules:: Failing portably in rules
* Special Chars in Names:: Special Characters in Macro Names
* Backslash-Newline-Empty:: Empty lines after backslash-newline
* Backslash-Newline Comments:: Spanning comments across line boundaries
* Long Lines in Makefiles:: Line length limitations
* Macros and Submakes:: `make macro=value' and submakes
* The Make Macro MAKEFLAGS:: `$(MAKEFLAGS)' portability issues
* The Make Macro SHELL:: `$(SHELL)' portability issues
* Parallel Make:: Parallel `make' quirks
* Comments in Make Rules:: Other problems with Make comments
* Newlines in Make Rules:: Using literal newlines in rules
* Comments in Make Macros:: Other problems with Make comments in macros
* Trailing whitespace in Make Macros:: Macro substitution problems
* Command-line Macros and whitespace:: Whitespace trimming of values
* obj/ and Make:: Don't name a subdirectory `obj'
* make -k Status:: Exit status of `make -k'
* VPATH and Make:: `VPATH' woes
* Single Suffix Rules:: Single suffix rules and separated dependencies
* Timestamps and Make:: Subsecond timestamp resolution
`VPATH' and Make
* Variables listed in VPATH:: `VPATH' must be literal on ancient hosts
* VPATH and Double-colon:: Problems with `::' on ancient hosts
* $< in Explicit Rules:: `$
File: autoconf.info, Node: Introduction, Next: The GNU Build System, Prev: Top, Up: Top
1 Introduction
**************
A physicist, an engineer, and a computer scientist were discussing the
nature of God. "Surely a Physicist," said the physicist, "because
early in the Creation, God made Light; and you know, Maxwell's
equations, the dual nature of electromagnetic waves, the relativistic
consequences..." "An Engineer!," said the engineer, "because
before making Light, God split the Chaos into Land and Water; it takes a
hell of an engineer to handle that big amount of mud, and orderly
separation of solids from liquids..." The computer scientist
shouted: "And the Chaos, where do you think it was coming from, hmm?"
--Anonymous
Autoconf is a tool for producing shell scripts that automatically
configure software source code packages to adapt to many kinds of
Posix-like systems. The configuration scripts produced by Autoconf are
independent of Autoconf when they are run, so their users do not need
to have Autoconf.
The configuration scripts produced by Autoconf require no manual user
intervention when run; they do not normally even need an argument
specifying the system type. Instead, they individually test for the
presence of each feature that the software package they are for might
need. (Before each check, they print a one-line message stating what
they are checking for, so the user doesn't get too bored while waiting
for the script to finish.) As a result, they deal well with systems
that are hybrids or customized from the more common Posix variants.
There is no need to maintain files that list the features supported by
each release of each variant of Posix.
For each software package that Autoconf is used with, it creates a
configuration script from a template file that lists the system features
that the package needs or can use. After the shell code to recognize
and respond to a system feature has been written, Autoconf allows it to
be shared by many software packages that can use (or need) that feature.
If it later turns out that the shell code needs adjustment for some
reason, it needs to be changed in only one place; all of the
configuration scripts can be regenerated automatically to take advantage
of the updated code.
Those who do not understand Autoconf are condemned to reinvent it,
poorly. The primary goal of Autoconf is making the _user's_ life
easier; making the _maintainer's_ life easier is only a secondary goal.
Put another way, the primary goal is not to make the generation of
`configure' automatic for package maintainers (although patches along
that front are welcome, since package maintainers form the user base of
Autoconf); rather, the goal is to make `configure' painless, portable,
and predictable for the end user of each "autoconfiscated" package.
And to this degree, Autoconf is highly successful at its goal -- most
complaints to the Autoconf list are about difficulties in writing
Autoconf input, and not in the behavior of the resulting `configure'.
Even packages that don't use Autoconf will generally provide a
`configure' script, and the most common complaint about these
alternative home-grown scripts is that they fail to meet one or more of
the GNU Coding Standards (*note Configuration:
(standards)Configuration.) that users have come to expect from
Autoconf-generated `configure' scripts.
The Metaconfig package is similar in purpose to Autoconf, but the
scripts it produces require manual user intervention, which is quite
inconvenient when configuring large source trees. Unlike Metaconfig
scripts, Autoconf scripts can support cross-compiling, if some care is
taken in writing them.
Autoconf does not solve all problems related to making portable
software packages--for a more complete solution, it should be used in
concert with other GNU build tools like Automake and Libtool. These
other tools take on jobs like the creation of a portable, recursive
makefile with all of the standard targets, linking of shared libraries,
and so on. *Note The GNU Build System::, for more information.
Autoconf imposes some restrictions on the names of macros used with
`#if' in C programs (*note Preprocessor Symbol Index::).
Autoconf requires GNU M4 version 1.4.6 or later in order to generate
the scripts. It uses features that some versions of M4, including GNU
M4 1.3, do not have. Autoconf works better with GNU M4 version 1.4.14
or later, though this is not required.
*Note Autoconf 1::, for information about upgrading from version 1.
*Note History::, for the story of Autoconf's development. *Note FAQ::,
for answers to some common questions about Autoconf.
See the Autoconf web page (http://www.gnu.org/software/autoconf/)
for up-to-date information, details on the mailing lists, pointers to a
list of known bugs, etc.
Mail suggestions to the Autoconf mailing list .
Past suggestions are archived
(http://lists.gnu.org/archive/html/autoconf/).
Mail bug reports to the Autoconf Bugs mailing list
. Past bug reports are archived
(http://lists.gnu.org/archive/html/bug-autoconf/).
If possible, first check that your bug is not already solved in
current development versions, and that it has not been reported yet.
Be sure to include all the needed information and a short
`configure.ac' that demonstrates the problem.
Autoconf's development tree is accessible via `git'; see the
Autoconf Summary (http://savannah.gnu.org/projects/autoconf/) for
details, or view the actual repository
(http://git.sv.gnu.org/gitweb/?p=autoconf.git). Anonymous CVS access
is also available, see `README' for more details. Patches relative to
the current `git' version can be sent for review to the Autoconf
Patches mailing list , with discussion on
prior patches archived
(http://lists.gnu.org/archive/html/autoconf-patches/); and all commits
are posted in the read-only Autoconf Commit mailing list
, which is also archived
(http://lists.gnu.org/archive/html/autoconf-commit/).
Because of its mission, the Autoconf package itself includes only a
set of often-used macros that have already demonstrated their
usefulness. Nevertheless, if you wish to share your macros, or find
existing ones, see the Autoconf Macro Archive
(http://www.gnu.org/software/autoconf-archive/), which is kindly run by
Peter Simons .
File: autoconf.info, Node: The GNU Build System, Next: Making configure Scripts, Prev: Introduction, Up: Top
2 The GNU Build System
**********************
Autoconf solves an important problem--reliable discovery of
system-specific build and runtime information--but this is only one
piece of the puzzle for the development of portable software. To this
end, the GNU project has developed a suite of integrated utilities to
finish the job Autoconf started: the GNU build system, whose most
important components are Autoconf, Automake, and Libtool. In this
chapter, we introduce you to those tools, point you to sources of more
information, and try to convince you to use the entire GNU build system
for your software.
* Menu:
* Automake:: Escaping makefile hell
* Gnulib:: The GNU portability library
* Libtool:: Building libraries portably
* Pointers:: More info on the GNU build system
File: autoconf.info, Node: Automake, Next: Gnulib, Up: The GNU Build System
2.1 Automake
============
The ubiquity of `make' means that a makefile is almost the only viable
way to distribute automatic build rules for software, but one quickly
runs into its numerous limitations. Its lack of support for automatic
dependency tracking, recursive builds in subdirectories, reliable
timestamps (e.g., for network file systems), and so on, mean that
developers must painfully (and often incorrectly) reinvent the wheel
for each project. Portability is non-trivial, thanks to the quirks of
`make' on many systems. On top of all this is the manual labor
required to implement the many standard targets that users have come to
expect (`make install', `make distclean', `make uninstall', etc.).
Since you are, of course, using Autoconf, you also have to insert
repetitive code in your `Makefile.in' to recognize `@CC@', `@CFLAGS@',
and other substitutions provided by `configure'. Into this mess steps
"Automake".
Automake allows you to specify your build needs in a `Makefile.am'
file with a vastly simpler and more powerful syntax than that of a plain
makefile, and then generates a portable `Makefile.in' for use with
Autoconf. For example, the `Makefile.am' to build and install a simple
"Hello world" program might look like:
bin_PROGRAMS = hello
hello_SOURCES = hello.c
The resulting `Makefile.in' (~400 lines) automatically supports all the
standard targets, the substitutions provided by Autoconf, automatic
dependency tracking, `VPATH' building, and so on. `make' builds the
`hello' program, and `make install' installs it in `/usr/local/bin' (or
whatever prefix was given to `configure', if not `/usr/local').
The benefits of Automake increase for larger packages (especially
ones with subdirectories), but even for small programs the added
convenience and portability can be substantial. And that's not all...
File: autoconf.info, Node: Gnulib, Next: Libtool, Prev: Automake, Up: The GNU Build System
2.2 Gnulib
==========
GNU software has a well-deserved reputation for running on many
different types of systems. While our primary goal is to write
software for the GNU system, many users and developers have been
introduced to us through the systems that they were already using.
Gnulib is a central location for common GNU code, intended to be
shared among free software packages. Its components are typically
shared at the source level, rather than being a library that gets built,
installed, and linked against. The idea is to copy files from Gnulib
into your own source tree. There is no distribution tarball; developers
should just grab source modules from the repository. The source files
are available online, under various licenses, mostly GNU GPL or GNU
LGPL.
Gnulib modules typically contain C source code along with Autoconf
macros used to configure the source code. For example, the Gnulib
`stdbool' module implements a `stdbool.h' header that nearly conforms
to C99, even on old-fashioned hosts that lack `stdbool.h'. This module
contains a source file for the replacement header, along with an
Autoconf macro that arranges to use the replacement header on
old-fashioned systems.
File: autoconf.info, Node: Libtool, Next: Pointers, Prev: Gnulib, Up: The GNU Build System
2.3 Libtool
===========
Often, one wants to build not only programs, but libraries, so that
other programs can benefit from the fruits of your labor. Ideally, one
would like to produce _shared_ (dynamically linked) libraries, which
can be used by multiple programs without duplication on disk or in
memory and can be updated independently of the linked programs.
Producing shared libraries portably, however, is the stuff of
nightmares--each system has its own incompatible tools, compiler flags,
and magic incantations. Fortunately, GNU provides a solution:
"Libtool".
Libtool handles all the requirements of building shared libraries for
you, and at this time seems to be the _only_ way to do so with any
portability. It also handles many other headaches, such as: the
interaction of Make rules with the variable suffixes of shared
libraries, linking reliably with shared libraries before they are
installed by the superuser, and supplying a consistent versioning system
(so that different versions of a library can be installed or upgraded
without breaking binary compatibility). Although Libtool, like
Autoconf, can be used without Automake, it is most simply utilized in
conjunction with Automake--there, Libtool is used automatically
whenever shared libraries are needed, and you need not know its syntax.
File: autoconf.info, Node: Pointers, Prev: Libtool, Up: The GNU Build System
2.4 Pointers
============
Developers who are used to the simplicity of `make' for small projects
on a single system might be daunted at the prospect of learning to use
Automake and Autoconf. As your software is distributed to more and
more users, however, you otherwise quickly find yourself putting lots
of effort into reinventing the services that the GNU build tools
provide, and making the same mistakes that they once made and overcame.
(Besides, since you're already learning Autoconf, Automake is a piece
of cake.)
There are a number of places that you can go to for more information
on the GNU build tools.
- Web
The project home pages for Autoconf
(http://www.gnu.org/software/autoconf/), Automake
(http://www.gnu.org/software/automake/), Gnulib
(http://www.gnu.org/software/gnulib/), and Libtool
(http://www.gnu.org/software/libtool/).
- Automake Manual
*Note Automake: (automake)Top, for more information on Automake.
- Books
The book `GNU Autoconf, Automake and Libtool'(1) describes the
complete GNU build environment. You can also find the entire book
on-line (http://sources.redhat.com/autobook/).
---------- Footnotes ----------
(1) `GNU Autoconf, Automake and Libtool', by G. V. Vaughan, B.
Elliston, T. Tromey, and I. L. Taylor. SAMS (originally New Riders),
2000, ISBN 1578701902.
File: autoconf.info, Node: Making configure Scripts, Next: Setup, Prev: The GNU Build System, Up: Top
3 Making `configure' Scripts
****************************
The configuration scripts that Autoconf produces are by convention
called `configure'. When run, `configure' creates several files,
replacing configuration parameters in them with appropriate values.
The files that `configure' creates are:
- one or more `Makefile' files, usually one in each subdirectory of
the package (*note Makefile Substitutions::);
- optionally, a C header file, the name of which is configurable,
containing `#define' directives (*note Configuration Headers::);
- a shell script called `config.status' that, when run, recreates
the files listed above (*note config.status Invocation::);
- an optional shell script normally called `config.cache' (created
when using `configure --config-cache') that saves the results of
running many of the tests (*note Cache Files::);
- a file called `config.log' containing any messages produced by
compilers, to help debugging if `configure' makes a mistake.
To create a `configure' script with Autoconf, you need to write an
Autoconf input file `configure.ac' (or `configure.in') and run
`autoconf' on it. If you write your own feature tests to supplement
those that come with Autoconf, you might also write files called
`aclocal.m4' and `acsite.m4'. If you use a C header file to contain
`#define' directives, you might also run `autoheader', and you can
distribute the generated file `config.h.in' with the package.
Here is a diagram showing how the files that can be used in
configuration are produced. Programs that are executed are suffixed by
`*'. Optional files are enclosed in square brackets (`[]').
`autoconf' and `autoheader' also read the installed Autoconf macro
files (by reading `autoconf.m4').
Files used in preparing a software package for distribution, when using
just Autoconf:
your source files --> [autoscan*] --> [configure.scan] --> configure.ac
configure.ac --.
| .------> autoconf* -----> configure
[aclocal.m4] --+---+
| `-----> [autoheader*] --> [config.h.in]
[acsite.m4] ---'
Makefile.in
Additionally, if you use Automake, the following additional productions
come into play:
[acinclude.m4] --.
|
[local macros] --+--> aclocal* --> aclocal.m4
|
configure.ac ----'
configure.ac --.
+--> automake* --> Makefile.in
Makefile.am ---'
Files used in configuring a software package:
.-------------> [config.cache]
configure* ------------+-------------> config.log
|
[config.h.in] -. v .-> [config.h] -.
+--> config.status* -+ +--> make*
Makefile.in ---' `-> Makefile ---'
* Menu:
* Writing Autoconf Input:: What to put in an Autoconf input file
* autoscan Invocation:: Semi-automatic `configure.ac' writing
* ifnames Invocation:: Listing the conditionals in source code
* autoconf Invocation:: How to create configuration scripts
* autoreconf Invocation:: Remaking multiple `configure' scripts
File: autoconf.info, Node: Writing Autoconf Input, Next: autoscan Invocation, Up: Making configure Scripts
3.1 Writing `configure.ac'
==========================
To produce a `configure' script for a software package, create a file
called `configure.ac' that contains invocations of the Autoconf macros
that test the system features your package needs or can use. Autoconf
macros already exist to check for many features; see *note Existing
Tests::, for their descriptions. For most other features, you can use
Autoconf template macros to produce custom checks; see *note Writing
Tests::, for information about them. For especially tricky or
specialized features, `configure.ac' might need to contain some
hand-crafted shell commands; see *note Portable Shell Programming:
Portable Shell. The `autoscan' program can give you a good start in
writing `configure.ac' (*note autoscan Invocation::, for more
information).
Previous versions of Autoconf promoted the name `configure.in',
which is somewhat ambiguous (the tool needed to process this file is not
described by its extension), and introduces a slight confusion with
`config.h.in' and so on (for which `.in' means "to be processed by
`configure'"). Using `configure.ac' is now preferred.
* Menu:
* Shell Script Compiler:: Autoconf as solution of a problem
* Autoconf Language:: Programming in Autoconf
* Autoconf Input Layout:: Standard organization of `configure.ac'
File: autoconf.info, Node: Shell Script Compiler, Next: Autoconf Language, Up: Writing Autoconf Input
3.1.1 A Shell Script Compiler
-----------------------------
Just as for any other computer language, in order to properly program
`configure.ac' in Autoconf you must understand _what_ problem the
language tries to address and _how_ it does so.
The problem Autoconf addresses is that the world is a mess. After
all, you are using Autoconf in order to have your package compile
easily on all sorts of different systems, some of them being extremely
hostile. Autoconf itself bears the price for these differences:
`configure' must run on all those systems, and thus `configure' must
limit itself to their lowest common denominator of features.
Naturally, you might then think of shell scripts; who needs
`autoconf'? A set of properly written shell functions is enough to
make it easy to write `configure' scripts by hand. Sigh!
Unfortunately, even in 2008, where shells without any function support
are far and few between, there are pitfalls to avoid when making use of
them. Also, finding a Bourne shell that accepts shell functions is not
trivial, even though there is almost always one on interesting porting
targets.
So, what is really needed is some kind of compiler, `autoconf', that
takes an Autoconf program, `configure.ac', and transforms it into a
portable shell script, `configure'.
How does `autoconf' perform this task?
There are two obvious possibilities: creating a brand new language or
extending an existing one. The former option is attractive: all sorts
of optimizations could easily be implemented in the compiler and many
rigorous checks could be performed on the Autoconf program (e.g.,
rejecting any non-portable construct). Alternatively, you can extend
an existing language, such as the `sh' (Bourne shell) language.
Autoconf does the latter: it is a layer on top of `sh'. It was
therefore most convenient to implement `autoconf' as a macro expander:
a program that repeatedly performs "macro expansions" on text input,
replacing macro calls with macro bodies and producing a pure `sh'
script in the end. Instead of implementing a dedicated Autoconf macro
expander, it is natural to use an existing general-purpose macro
language, such as M4, and implement the extensions as a set of M4
macros.
File: autoconf.info, Node: Autoconf Language, Next: Autoconf Input Layout, Prev: Shell Script Compiler, Up: Writing Autoconf Input
3.1.2 The Autoconf Language
---------------------------
The Autoconf language differs from many other computer languages
because it treats actual code the same as plain text. Whereas in C,
for instance, data and instructions have different syntactic status, in
Autoconf their status is rigorously the same. Therefore, we need a
means to distinguish literal strings from text to be expanded:
quotation.
When calling macros that take arguments, there must not be any white
space between the macro name and the open parenthesis.
AC_INIT ([oops], [1.0]) # incorrect
AC_INIT([hello], [1.0]) # good
Arguments should be enclosed within the quote characters `[' and
`]', and be separated by commas. Any leading blanks or newlines in
arguments are ignored, unless they are quoted. You should always quote
an argument that might contain a macro name, comma, parenthesis, or a
leading blank or newline. This rule applies recursively for every macro
call, including macros called from other macros. For more details on
quoting rules, see *note Programming in M4::.
For instance:
AC_CHECK_HEADER([stdio.h],
[AC_DEFINE([HAVE_STDIO_H], [1],
[Define to 1 if you have .])],
[AC_MSG_ERROR([sorry, can't do anything for you])])
is quoted properly. You may safely simplify its quotation to:
AC_CHECK_HEADER([stdio.h],
[AC_DEFINE([HAVE_STDIO_H], 1,
[Define to 1 if you have .])],
[AC_MSG_ERROR([sorry, can't do anything for you])])
because `1' cannot contain a macro call. Here, the argument of
`AC_MSG_ERROR' must be quoted; otherwise, its comma would be
interpreted as an argument separator. Also, the second and third
arguments of `AC_CHECK_HEADER' must be quoted, since they contain macro
calls. The three arguments `HAVE_STDIO_H', `stdio.h', and `Define to 1
if you have .' do not need quoting, but if you unwisely
defined a macro with a name like `Define' or `stdio' then they would
need quoting. Cautious Autoconf users would keep the quotes, but many
Autoconf users find such precautions annoying, and would rewrite the
example as follows:
AC_CHECK_HEADER(stdio.h,
[AC_DEFINE(HAVE_STDIO_H, 1,
[Define to 1 if you have .])],
[AC_MSG_ERROR([sorry, can't do anything for you])])
This is safe, so long as you adopt good naming conventions and do not
define macros with names like `HAVE_STDIO_H', `stdio', or `h'. Though
it is also safe here to omit the quotes around `Define to 1 if you have
.' this is not recommended, as message strings are more likely
to inadvertently contain commas.
The following example is wrong and dangerous, as it is underquoted:
AC_CHECK_HEADER(stdio.h,
AC_DEFINE(HAVE_STDIO_H, 1,
Define to 1 if you have .),
AC_MSG_ERROR([sorry, can't do anything for you]))
In other cases, you may have to use text that also resembles a macro
call. You must quote that text even when it is not passed as a macro
argument. For example, these two approaches in `configure.ac' (quoting
just the potential problems, or quoting the entire line) will protect
your script in case autoconf ever adds a macro `AC_DC':
echo "Hard rock was here! --[AC_DC]"
[echo "Hard rock was here! --AC_DC"]
which results in this text in `configure':
echo "Hard rock was here! --AC_DC"
echo "Hard rock was here! --AC_DC"
When you use the same text in a macro argument, you must therefore have
an extra quotation level (since one is stripped away by the macro
substitution). In general, then, it is a good idea to _use double
quoting for all literal string arguments_, either around just the
problematic portions, or over the entire argument:
AC_MSG_WARN([[AC_DC] stinks --Iron Maiden])
AC_MSG_WARN([[AC_DC stinks --Iron Maiden]])
However, the above example triggers a warning about a possibly
unexpanded macro when running `autoconf', because it collides with the
namespace of macros reserved for the Autoconf language. To be really
safe, you can use additional escaping (either a quadrigraph, or
creative shell constructs) to silence that particular warning:
echo "Hard rock was here! --AC""_DC"
AC_MSG_WARN([[AC@&t@_DC stinks --Iron Maiden]])
You are now able to understand one of the constructs of Autoconf that
has been continually misunderstood... The rule of thumb is that
_whenever you expect macro expansion, expect quote expansion_; i.e.,
expect one level of quotes to be lost. For instance:
AC_COMPILE_IFELSE(AC_LANG_SOURCE([char b[10];]), [],
[AC_MSG_ERROR([you lose])])
is incorrect: here, the first argument of `AC_LANG_SOURCE' is `char
b[10];' and is expanded once, which results in `char b10;'; and the
`AC_LANG_SOURCE' is also expanded prior to being passed to
`AC_COMPILE_IFELSE'. (There was an idiom common in Autoconf's past to
address this issue via the M4 `changequote' primitive, but do not use
it!) Let's take a closer look: the author meant the first argument to
be understood as a literal, and therefore it must be quoted twice;
likewise, the intermediate `AC_LANG_SOURCE' macro should be quoted once
so that it is only expanded after the rest of the body of
`AC_COMPILE_IFELSE' is in place:
AC_COMPILE_IFELSE([AC_LANG_SOURCE([[char b[10];]])], [],
[AC_MSG_ERROR([you lose])])
Voila`, you actually produce `char b[10];' this time!
On the other hand, descriptions (e.g., the last parameter of
`AC_DEFINE' or `AS_HELP_STRING') are not literals--they are subject to
line breaking, for example--and should not be double quoted. Even if
these descriptions are short and are not actually broken, double
quoting them yields weird results.
Some macros take optional arguments, which this documentation
represents as [ARG] (not to be confused with the quote characters).
You may just leave them empty, or use `[]' to make the emptiness of the
argument explicit, or you may simply omit the trailing commas. The
three lines below are equivalent:
AC_CHECK_HEADERS([stdio.h], [], [], [])
AC_CHECK_HEADERS([stdio.h],,,)
AC_CHECK_HEADERS([stdio.h])
It is best to put each macro call on its own line in `configure.ac'.
Most of the macros don't add extra newlines; they rely on the newline
after the macro call to terminate the commands. This approach makes
the generated `configure' script a little easier to read by not
inserting lots of blank lines. It is generally safe to set shell
variables on the same line as a macro call, because the shell allows
assignments without intervening newlines.
You can include comments in `configure.ac' files by starting them
with the `#'. For example, it is helpful to begin `configure.ac' files
with a line like this:
# Process this file with autoconf to produce a configure script.
File: autoconf.info, Node: Autoconf Input Layout, Prev: Autoconf Language, Up: Writing Autoconf Input
3.1.3 Standard `configure.ac' Layout
------------------------------------
The order in which `configure.ac' calls the Autoconf macros is not
important, with a few exceptions. Every `configure.ac' must contain a
call to `AC_INIT' before the checks, and a call to `AC_OUTPUT' at the
end (*note Output::). Additionally, some macros rely on other macros
having been called first, because they check previously set values of
some variables to decide what to do. These macros are noted in the
individual descriptions (*note Existing Tests::), and they also warn
you when `configure' is created if they are called out of order.
To encourage consistency, here is a suggested order for calling the
Autoconf macros. Generally speaking, the things near the end of this
list are those that could depend on things earlier in it. For example,
library functions could be affected by types and libraries.
Autoconf requirements
`AC_INIT(PACKAGE, VERSION, BUG-REPORT-ADDRESS)'
information on the package
checks for programs
checks for libraries
checks for header files
checks for types
checks for structures
checks for compiler characteristics
checks for library functions
checks for system services
`AC_CONFIG_FILES([FILE...])'
`AC_OUTPUT'
File: autoconf.info, Node: autoscan Invocation, Next: ifnames Invocation, Prev: Writing Autoconf Input, Up: Making configure Scripts
3.2 Using `autoscan' to Create `configure.ac'
=============================================
The `autoscan' program can help you create and/or maintain a
`configure.ac' file for a software package. `autoscan' examines source
files in the directory tree rooted at a directory given as a command
line argument, or the current directory if none is given. It searches
the source files for common portability problems and creates a file
`configure.scan' which is a preliminary `configure.ac' for that
package, and checks a possibly existing `configure.ac' for completeness.
When using `autoscan' to create a `configure.ac', you should
manually examine `configure.scan' before renaming it to `configure.ac';
it probably needs some adjustments. Occasionally, `autoscan' outputs a
macro in the wrong order relative to another macro, so that `autoconf'
produces a warning; you need to move such macros manually. Also, if
you want the package to use a configuration header file, you must add a
call to `AC_CONFIG_HEADERS' (*note Configuration Headers::). You might
also have to change or add some `#if' directives to your program in
order to make it work with Autoconf (*note ifnames Invocation::, for
information about a program that can help with that job).
When using `autoscan' to maintain a `configure.ac', simply consider
adding its suggestions. The file `autoscan.log' contains detailed
information on why a macro is requested.
`autoscan' uses several data files (installed along with Autoconf)
to determine which macros to output when it finds particular symbols in
a package's source files. These data files all have the same format:
each line consists of a symbol, one or more blanks, and the Autoconf
macro to output if that symbol is encountered. Lines starting with `#'
are comments.
`autoscan' accepts the following options:
`--help'
`-h'
Print a summary of the command line options and exit.
`--version'
`-V'
Print the version number of Autoconf and exit.
`--verbose'
`-v'
Print the names of the files it examines and the potentially
interesting symbols it finds in them. This output can be
voluminous.
`--debug'
`-d'
Don't remove temporary files.
`--include=DIR'
`-I DIR'
Append DIR to the include path. Multiple invocations accumulate.
`--prepend-include=DIR'
`-B DIR'
Prepend DIR to the include path. Multiple invocations accumulate.
File: autoconf.info, Node: ifnames Invocation, Next: autoconf Invocation, Prev: autoscan Invocation, Up: Making configure Scripts
3.3 Using `ifnames' to List Conditionals
========================================
`ifnames' can help you write `configure.ac' for a software package. It
prints the identifiers that the package already uses in C preprocessor
conditionals. If a package has already been set up to have some
portability, `ifnames' can thus help you figure out what its
`configure' needs to check for. It may help fill in some gaps in a
`configure.ac' generated by `autoscan' (*note autoscan Invocation::).
`ifnames' scans all of the C source files named on the command line
(or the standard input, if none are given) and writes to the standard
output a sorted list of all the identifiers that appear in those files
in `#if', `#elif', `#ifdef', or `#ifndef' directives. It prints each
identifier on a line, followed by a space-separated list of the files
in which that identifier occurs.
`ifnames' accepts the following options:
`--help'
`-h'
Print a summary of the command line options and exit.
`--version'
`-V'
Print the version number of Autoconf and exit.
File: autoconf.info, Node: autoconf Invocation, Next: autoreconf Invocation, Prev: ifnames Invocation, Up: Making configure Scripts
3.4 Using `autoconf' to Create `configure'
==========================================
To create `configure' from `configure.ac', run the `autoconf' program
with no arguments. `autoconf' processes `configure.ac' with the M4
macro processor, using the Autoconf macros. If you give `autoconf' an
argument, it reads that file instead of `configure.ac' and writes the
configuration script to the standard output instead of to `configure'.
If you give `autoconf' the argument `-', it reads from the standard
input instead of `configure.ac' and writes the configuration script to
the standard output.
The Autoconf macros are defined in several files. Some of the files
are distributed with Autoconf; `autoconf' reads them first. Then it
looks for the optional file `acsite.m4' in the directory that contains
the distributed Autoconf macro files, and for the optional file
`aclocal.m4' in the current directory. Those files can contain your
site's or the package's own Autoconf macro definitions (*note Writing
Autoconf Macros::, for more information). If a macro is defined in
more than one of the files that `autoconf' reads, the last definition
it reads overrides the earlier ones.
`autoconf' accepts the following options:
`--help'
`-h'
Print a summary of the command line options and exit.
`--version'
`-V'
Print the version number of Autoconf and exit.
`--verbose'
`-v'
Report processing steps.
`--debug'
`-d'
Don't remove the temporary files.
`--force'
`-f'
Remake `configure' even if newer than its input files.
`--include=DIR'
`-I DIR'
Append DIR to the include path. Multiple invocations accumulate.
`--prepend-include=DIR'
`-B DIR'
Prepend DIR to the include path. Multiple invocations accumulate.
`--output=FILE'
`-o FILE'
Save output (script or trace) to FILE. The file `-' stands for
the standard output.
`--warnings=CATEGORY'
`-W CATEGORY'
Report the warnings related to CATEGORY (which can actually be a
comma separated list). *Note Reporting Messages::, macro
`AC_DIAGNOSE', for a comprehensive list of categories. Special
values include:
`all'
report all the warnings
`none'
report none
`error'
treats warnings as errors
`no-CATEGORY'
disable warnings falling into CATEGORY
Warnings about `syntax' are enabled by default, and the environment
variable `WARNINGS', a comma separated list of categories, is
honored as well. Passing `-W CATEGORY' actually behaves as if you
had passed `--warnings syntax,$WARNINGS,CATEGORY'. To disable the
defaults and `WARNINGS', and then enable warnings about obsolete
constructs, use `-W none,obsolete'.
Because `autoconf' uses `autom4te' behind the scenes, it displays
a back trace for errors, but not for warnings; if you want them,
just pass `-W error'. *Note autom4te Invocation::, for some
examples.
`--trace=MACRO[:FORMAT]'
`-t MACRO[:FORMAT]'
Do not create the `configure' script, but list the calls to MACRO
according to the FORMAT. Multiple `--trace' arguments can be used
to list several macros. Multiple `--trace' arguments for a single
macro are not cumulative; instead, you should just make FORMAT as
long as needed.
The FORMAT is a regular string, with newlines if desired, and
several special escape codes. It defaults to `$f:$l:$n:$%'; see
*note autom4te Invocation::, for details on the FORMAT.
`--initialization'
`-i'
By default, `--trace' does not trace the initialization of the
Autoconf macros (typically the `AC_DEFUN' definitions). This
results in a noticeable speedup, but can be disabled by this
option.
It is often necessary to check the content of a `configure.ac' file,
but parsing it yourself is extremely fragile and error-prone. It is
suggested that you rely upon `--trace' to scan `configure.ac'. For
instance, to find the list of variables that are substituted, use:
$ autoconf -t AC_SUBST
configure.ac:2:AC_SUBST:ECHO_C
configure.ac:2:AC_SUBST:ECHO_N
configure.ac:2:AC_SUBST:ECHO_T
More traces deleted
The example below highlights the difference between `$@', `$*', and
`$%'.
$ cat configure.ac
AC_DEFINE(This, is, [an
[example]])
$ autoconf -t 'AC_DEFINE:@: $@
*: $*
%: $%'
@: [This],[is],[an
[example]]
*: This,is,an
[example]
%: This:is:an [example]
The FORMAT gives you a lot of freedom:
$ autoconf -t 'AC_SUBST:$$ac_subst{"$1"} = "$f:$l";'
$ac_subst{"ECHO_C"} = "configure.ac:2";
$ac_subst{"ECHO_N"} = "configure.ac:2";
$ac_subst{"ECHO_T"} = "configure.ac:2";
More traces deleted
A long SEPARATOR can be used to improve the readability of complex
structures, and to ease their parsing (for instance when no single
character is suitable as a separator):
$ autoconf -t 'AM_MISSING_PROG:${|:::::|}*'
ACLOCAL|:::::|aclocal|:::::|$missing_dir
AUTOCONF|:::::|autoconf|:::::|$missing_dir
AUTOMAKE|:::::|automake|:::::|$missing_dir
More traces deleted
File: autoconf.info, Node: autoreconf Invocation, Prev: autoconf Invocation, Up: Making configure Scripts
3.5 Using `autoreconf' to Update `configure' Scripts
====================================================
Installing the various components of the GNU Build System can be
tedious: running `autopoint' for Gettext, `automake' for `Makefile.in'
etc. in each directory. It may be needed either because some tools
such as `automake' have been updated on your system, or because some of
the sources such as `configure.ac' have been updated, or finally,
simply in order to install the GNU Build System in a fresh tree.
`autoreconf' runs `autoconf', `autoheader', `aclocal', `automake',
`libtoolize', and `autopoint' (when appropriate) repeatedly to update
the GNU Build System in the specified directories and their
subdirectories (*note Subdirectories::). By default, it only remakes
those files that are older than their sources. The environment
variables `AUTOM4TE', `AUTOCONF', `AUTOHEADER', `AUTOMAKE', `ACLOCAL',
`AUTOPOINT', `LIBTOOLIZE', `M4', and `MAKE' may be used to override the
invocation of the respective tools.
If you install a new version of some tool, you can make `autoreconf'
remake _all_ of the files by giving it the `--force' option.
*Note Automatic Remaking::, for Make rules to automatically rebuild
`configure' scripts when their source files change. That method
handles the timestamps of configuration header templates properly, but
does not pass `--autoconf-dir=DIR' or `--localdir=DIR'.
Gettext supplies the `autopoint' command to add translation
infrastructure to a source package. If you use `autopoint', your
`configure.ac' should invoke both `AM_GNU_GETTEXT' and
`AM_GNU_GETTEXT_VERSION(GETTEXT-VERSION)'. *Note Invoking the
`autopoint' Program: (gettext)autopoint Invocation, for further details.
`autoreconf' accepts the following options:
`--help'
`-h'
Print a summary of the command line options and exit.
`--version'
`-V'
Print the version number of Autoconf and exit.
`--verbose'
`-v'
Print the name of each directory `autoreconf' examines and the
commands it runs. If given two or more times, pass `--verbose' to
subordinate tools that support it.
`--debug'
`-d'
Don't remove the temporary files.
`--force'
`-f'
Remake even `configure' scripts and configuration headers that are
newer than their input files (`configure.ac' and, if present,
`aclocal.m4').
`--install'
`-i'
Install the missing auxiliary files in the package. By default,
files are copied; this can be changed with `--symlink'.
If deemed appropriate, this option triggers calls to `automake
--add-missing', `libtoolize', `autopoint', etc.
`--no-recursive'
Do not rebuild files in subdirectories to configure (see *note
Subdirectories::, macro `AC_CONFIG_SUBDIRS').
`--symlink'
`-s'
When used with `--install', install symbolic links to the missing
auxiliary files instead of copying them.
`--make'
`-m'
When the directories were configured, update the configuration by
running `./config.status --recheck && ./config.status', and then
run `make'.
`--include=DIR'
`-I DIR'
Append DIR to the include path. Multiple invocations accumulate.
Passed on to `aclocal', `autoconf' and `autoheader' internally.
`--prepend-include=DIR'
`-B DIR'
Prepend DIR to the include path. Multiple invocations accumulate.
Passed on to `autoconf' and `autoheader' internally.
`--warnings=CATEGORY'
`-W CATEGORY'
Report the warnings related to CATEGORY (which can actually be a
comma separated list).
`cross'
related to cross compilation issues.
`obsolete'
report the uses of obsolete constructs.
`portability'
portability issues
`syntax'
dubious syntactic constructs.
`all'
report all the warnings
`none'
report none
`error'
treats warnings as errors
`no-CATEGORY'
disable warnings falling into CATEGORY
Warnings about `syntax' are enabled by default, and the environment
variable `WARNINGS', a comma separated list of categories, is
honored as well. Passing `-W CATEGORY' actually behaves as if you
had passed `--warnings syntax,$WARNINGS,CATEGORY'. To disable the
defaults and `WARNINGS', and then enable warnings about obsolete
constructs, use `-W none,obsolete'.
If you want `autoreconf' to pass flags that are not listed here on
to `aclocal', set `ACLOCAL_AMFLAGS' in your `Makefile.am'. Due to a
limitation in the Autoconf implementation these flags currently must be
set on a single line in `Makefile.am', without any backslash-newlines.
File: autoconf.info, Node: Setup, Next: Existing Tests, Prev: Making configure Scripts, Up: Top
4 Initialization and Output Files
*********************************
Autoconf-generated `configure' scripts need some information about how
to initialize, such as how to find the package's source files and about
the output files to produce. The following sections describe the
initialization and the creation of output files.
* Menu:
* Initializing configure:: Option processing etc.
* Versioning:: Dealing with Autoconf versions
* Notices:: Copyright, version numbers in `configure'
* Input:: Where Autoconf should find files
* Output:: Outputting results from the configuration
* Configuration Actions:: Preparing the output based on results
* Configuration Files:: Creating output files
* Makefile Substitutions:: Using output variables in makefiles
* Configuration Headers:: Creating a configuration header file
* Configuration Commands:: Running arbitrary instantiation commands
* Configuration Links:: Links depending on the configuration
* Subdirectories:: Configuring independent packages together
* Default Prefix:: Changing the default installation prefix
File: autoconf.info, Node: Initializing configure, Next: Versioning, Up: Setup
4.1 Initializing `configure'
============================
Every `configure' script must call `AC_INIT' before doing anything else
that produces output. Calls to silent macros, such as `AC_DEFUN', may
also occur prior to `AC_INIT', although these are generally used via
`aclocal.m4', since that is implicitly included before the start of
`configure.ac'. The only other required macro is `AC_OUTPUT' (*note
Output::).
-- Macro: AC_INIT (PACKAGE, VERSION, [BUG-REPORT], [TARNAME], [URL])
Process any command-line arguments and perform initialization and
verification.
Set the name of the PACKAGE and its VERSION. These are typically
used in `--version' support, including that of `configure'. The
optional argument BUG-REPORT should be the email to which users
should send bug reports. The package TARNAME differs from
PACKAGE: the latter designates the full package name (e.g., `GNU
Autoconf'), while the former is meant for distribution tar ball
names (e.g., `autoconf'). It defaults to PACKAGE with `GNU '
stripped, lower-cased, and all characters other than alphanumerics
and underscores are changed to `-'. If provided, URL should be
the home page for the package.
The arguments of `AC_INIT' must be static, i.e., there should not
be any shell computation, quotes, or newlines, but they can be
computed by M4. This is because the package information strings
are expanded at M4 time into several contexts, and must give the
same text at shell time whether used in single-quoted strings,
double-quoted strings, quoted here-documents, or unquoted
here-documents. It is permissible to use `m4_esyscmd' or
`m4_esyscmd_s' for computing a version string that changes with
every commit to a version control system (in fact, Autoconf does
just that, for all builds of the development tree made between
releases).
The following M4 macros (e.g., `AC_PACKAGE_NAME'), output variables
(e.g., `PACKAGE_NAME'), and preprocessor symbols (e.g.,
`PACKAGE_NAME'), are defined by `AC_INIT':
`AC_PACKAGE_NAME', `PACKAGE_NAME'
Exactly PACKAGE.
`AC_PACKAGE_TARNAME', `PACKAGE_TARNAME'
Exactly TARNAME, possibly generated from PACKAGE.
`AC_PACKAGE_VERSION', `PACKAGE_VERSION'
Exactly VERSION.
`AC_PACKAGE_STRING', `PACKAGE_STRING'
Exactly `PACKAGE VERSION'.
`AC_PACKAGE_BUGREPORT', `PACKAGE_BUGREPORT'
Exactly BUG-REPORT, if one was provided. Typically an email
address, or URL to a bug management web page.
`AC_PACKAGE_URL', `PACKAGE_URL'
Exactly URL, if one was provided. If URL was empty, but
PACKAGE begins with `GNU ', then this defaults to
`http://www.gnu.org/software/TARNAME/', otherwise, no URL is
assumed.
If your `configure' script does its own option processing, it should
inspect `$@' or `$*' immediately after calling `AC_INIT', because other
Autoconf macros liberally use the `set' command to process strings, and
this has the side effect of updating `$@' and `$*'. However, we
suggest that you use standard macros like `AC_ARG_ENABLE' instead of
attempting to implement your own option processing. *Note Site
Configuration::.
File: autoconf.info, Node: Versioning, Next: Notices, Prev: Initializing configure, Up: Setup
4.2 Dealing with Autoconf versions
==================================
The following optional macros can be used to help choose the minimum
version of Autoconf that can successfully compile a given
`configure.ac'.
-- Macro: AC_PREREQ (VERSION)
Ensure that a recent enough version of Autoconf is being used. If
the version of Autoconf being used to create `configure' is
earlier than VERSION, print an error message to the standard error
output and exit with failure (exit status is 63). For example:
AC_PREREQ([2.69])
This macro may be used before `AC_INIT'.
-- Macro: AC_AUTOCONF_VERSION
This macro was introduced in Autoconf 2.62. It identifies the
version of Autoconf that is currently parsing the input file, in a
format suitable for `m4_version_compare' (*note
m4_version_compare::); in other words, for this release of
Autoconf, its value is `2.69'. One potential use of this macro is
for writing conditional fallbacks based on when a feature was
added to Autoconf, rather than using `AC_PREREQ' to require the
newer version of Autoconf. However, remember that the Autoconf
philosophy favors feature checks over version checks.
You should not expand this macro directly; use
`m4_defn([AC_AUTOCONF_VERSION])' instead. This is because some
users might have a beta version of Autoconf installed, with
arbitrary letters included in its version string. This means it
is possible for the version string to contain the name of a
defined macro, such that expanding `AC_AUTOCONF_VERSION' would
trigger the expansion of that macro during rescanning, and change
the version string to be different than what you intended to check.
File: autoconf.info, Node: Notices, Next: Input, Prev: Versioning, Up: Setup
4.3 Notices in `configure'
==========================
The following macros manage version numbers for `configure' scripts.
Using them is optional.
-- Macro: AC_COPYRIGHT (COPYRIGHT-NOTICE)
State that, in addition to the Free Software Foundation's
copyright on the Autoconf macros, parts of your `configure' are
covered by the COPYRIGHT-NOTICE.
The COPYRIGHT-NOTICE shows up in both the head of `configure' and
in `configure --version'.
-- Macro: AC_REVISION (REVISION-INFO)
Copy revision stamp REVISION-INFO into the `configure' script,
with any dollar signs or double-quotes removed. This macro lets
you put a revision stamp from `configure.ac' into `configure'
without RCS or CVS changing it when you check in `configure'.
That way, you can determine easily which revision of
`configure.ac' a particular `configure' corresponds to.
For example, this line in `configure.ac':
AC_REVISION([$Revision: 1.30 $])
produces this in `configure':
#!/bin/sh
# From configure.ac Revision: 1.30
File: autoconf.info, Node: Input, Next: Output, Prev: Notices, Up: Setup
4.4 Finding `configure' Input
=============================
-- Macro: AC_CONFIG_SRCDIR (UNIQUE-FILE-IN-SOURCE-DIR)
UNIQUE-FILE-IN-SOURCE-DIR is some file that is in the package's
source directory; `configure' checks for this file's existence to
make sure that the directory that it is told contains the source
code in fact does. Occasionally people accidentally specify the
wrong directory with `--srcdir'; this is a safety check. *Note
configure Invocation::, for more information.
Packages that do manual configuration or use the `install' program
might need to tell `configure' where to find some other shell scripts
by calling `AC_CONFIG_AUX_DIR', though the default places it looks are
correct for most cases.
-- Macro: AC_CONFIG_AUX_DIR (DIR)
Use the auxiliary build tools (e.g., `install-sh', `config.sub',
`config.guess', Cygnus `configure', Automake and Libtool scripts,
etc.) that are in directory DIR. These are auxiliary files used
in configuration. DIR can be either absolute or relative to
`SRCDIR'. The default is `SRCDIR' or `SRCDIR/..' or
`SRCDIR/../..', whichever is the first that contains `install-sh'.
The other files are not checked for, so that using
`AC_PROG_INSTALL' does not automatically require distributing the
other auxiliary files. It checks for `install.sh' also, but that
name is obsolete because some `make' have a rule that creates
`install' from it if there is no makefile.
The auxiliary directory is commonly named `build-aux'. If you
need portability to DOS variants, do not name the auxiliary
directory `aux'. *Note File System Conventions::.
-- Macro: AC_REQUIRE_AUX_FILE (FILE)
Declares that FILE is expected in the directory defined above. In
Autoconf proper, this macro does nothing: its sole purpose is to be
traced by third-party tools to produce a list of expected auxiliary
files. For instance it is called by macros like `AC_PROG_INSTALL'
(*note Particular Programs::) or `AC_CANONICAL_BUILD' (*note
Canonicalizing::) to register the auxiliary files they need.
Similarly, packages that use `aclocal' should declare where local
macros can be found using `AC_CONFIG_MACRO_DIR'.
-- Macro: AC_CONFIG_MACRO_DIR (DIR)
Specify DIR as the location of additional local Autoconf macros.
This macro is intended for use by future versions of commands like
`autoreconf' that trace macro calls. It should be called directly
from `configure.ac' so that tools that install macros for
`aclocal' can find the macros' declarations.
Note that if you use `aclocal' from Automake to generate
`aclocal.m4', you must also set `ACLOCAL_AMFLAGS = -I DIR' in your
top-level `Makefile.am'. Due to a limitation in the Autoconf
implementation of `autoreconf', these include directives currently
must be set on a single line in `Makefile.am', without any
backslash-newlines.
File: autoconf.info, Node: Output, Next: Configuration Actions, Prev: Input, Up: Setup
4.5 Outputting Files
====================
Every Autoconf script, e.g., `configure.ac', should finish by calling
`AC_OUTPUT'. That is the macro that generates and runs
`config.status', which in turn creates the makefiles and any other
files resulting from configuration. This is the only required macro
besides `AC_INIT' (*note Input::).
-- Macro: AC_OUTPUT
Generate `config.status' and launch it. Call this macro once, at
the end of `configure.ac'.
`config.status' performs all the configuration actions: all the
output files (see *note Configuration Files::, macro
`AC_CONFIG_FILES'), header files (see *note Configuration
Headers::, macro `AC_CONFIG_HEADERS'), commands (see *note
Configuration Commands::, macro `AC_CONFIG_COMMANDS'), links (see
*note Configuration Links::, macro `AC_CONFIG_LINKS'),
subdirectories to configure (see *note Subdirectories::, macro
`AC_CONFIG_SUBDIRS') are honored.
The location of your `AC_OUTPUT' invocation is the exact point
where configuration actions are taken: any code afterwards is
executed by `configure' once `config.status' was run. If you want
to bind actions to `config.status' itself (independently of
whether `configure' is being run), see *note Running Arbitrary
Configuration Commands: Configuration Commands.
Historically, the usage of `AC_OUTPUT' was somewhat different.
*Note Obsolete Macros::, for a description of the arguments that
`AC_OUTPUT' used to support.
If you run `make' in subdirectories, you should run it using the
`make' variable `MAKE'. Most versions of `make' set `MAKE' to the name
of the `make' program plus any options it was given. (But many do not
include in it the values of any variables set on the command line, so
those are not passed on automatically.) Some old versions of `make' do
not set this variable. The following macro allows you to use it even
with those versions.
-- Macro: AC_PROG_MAKE_SET
If the Make command, `$MAKE' if set or else `make', predefines
`$(MAKE)', define output variable `SET_MAKE' to be empty.
Otherwise, define `SET_MAKE' to a macro definition that sets
`$(MAKE)', such as `MAKE=make'. Calls `AC_SUBST' for `SET_MAKE'.
If you use this macro, place a line like this in each `Makefile.in'
that runs `MAKE' on other directories:
@SET_MAKE@
File: autoconf.info, Node: Configuration Actions, Next: Configuration Files, Prev: Output, Up: Setup
4.6 Performing Configuration Actions
====================================
`configure' is designed so that it appears to do everything itself, but
there is actually a hidden slave: `config.status'. `configure' is in
charge of examining your system, but it is `config.status' that
actually takes the proper actions based on the results of `configure'.
The most typical task of `config.status' is to _instantiate_ files.
This section describes the common behavior of the four standard
instantiating macros: `AC_CONFIG_FILES', `AC_CONFIG_HEADERS',
`AC_CONFIG_COMMANDS' and `AC_CONFIG_LINKS'. They all have this
prototype:
AC_CONFIG_ITEMS(TAG..., [COMMANDS], [INIT-CMDS])
where the arguments are:
TAG...
A blank-or-newline-separated list of tags, which are typically the
names of the files to instantiate.
You are encouraged to use literals as TAGS. In particular, you
should avoid
... && my_foos="$my_foos fooo"
... && my_foos="$my_foos foooo"
AC_CONFIG_ITEMS([$my_foos])
and use this instead:
... && AC_CONFIG_ITEMS([fooo])
... && AC_CONFIG_ITEMS([foooo])
The macros `AC_CONFIG_FILES' and `AC_CONFIG_HEADERS' use special
TAG values: they may have the form `OUTPUT' or `OUTPUT:INPUTS'.
The file OUTPUT is instantiated from its templates, INPUTS
(defaulting to `OUTPUT.in').
`AC_CONFIG_FILES([Makefile:boiler/top.mk:boiler/bot.mk])', for
example, asks for the creation of the file `Makefile' that
contains the expansion of the output variables in the
concatenation of `boiler/top.mk' and `boiler/bot.mk'.
The special value `-' might be used to denote the standard output
when used in OUTPUT, or the standard input when used in the
INPUTS. You most probably don't need to use this in
`configure.ac', but it is convenient when using the command line
interface of `./config.status', see *note config.status
Invocation::, for more details.
The INPUTS may be absolute or relative file names. In the latter
case they are first looked for in the build tree, and then in the
source tree. Input files should be text files, and a line length
below 2000 bytes should be safe.
COMMANDS
Shell commands output literally into `config.status', and
associated with a tag that the user can use to tell `config.status'
which commands to run. The commands are run each time a TAG
request is given to `config.status', typically each time the file
`TAG' is created.
The variables set during the execution of `configure' are _not_
available here: you first need to set them via the INIT-CMDS.
Nonetheless the following variables are precomputed:
`srcdir'
The name of the top source directory, assuming that the
working directory is the top build directory. This is what
the `configure' option `--srcdir' sets.
`ac_top_srcdir'
The name of the top source directory, assuming that the
working directory is the current build directory.
`ac_top_build_prefix'
The name of the top build directory, assuming that the working
directory is the current build directory. It can be empty,
or else ends with a slash, so that you may concatenate it.
`ac_srcdir'
The name of the corresponding source directory, assuming that
the working directory is the current build directory.
`tmp'
The name of a temporary directory within the build tree,
which you can use if you need to create additional temporary
files. The directory is cleaned up when `config.status' is
done or interrupted. Please use package-specific file name
prefixes to avoid clashing with files that `config.status'
may use internally.
The "current" directory refers to the directory (or
pseudo-directory) containing the input part of TAGS. For
instance, running
AC_CONFIG_COMMANDS([deep/dir/out:in/in.in], [...], [...])
with `--srcdir=../package' produces the following values:
# Argument of --srcdir
srcdir='../package'
# Reversing deep/dir
ac_top_build_prefix='../../'
# Concatenation of $ac_top_build_prefix and srcdir
ac_top_srcdir='../../../package'
# Concatenation of $ac_top_srcdir and deep/dir
ac_srcdir='../../../package/deep/dir'
independently of `in/in.in'.
INIT-CMDS
Shell commands output _unquoted_ near the beginning of
`config.status', and executed each time `config.status' runs
(regardless of the tag). Because they are unquoted, for example,
`$var' is output as the value of `var'. INIT-CMDS is typically
used by `configure' to give `config.status' some variables it
needs to run the COMMANDS.
You should be extremely cautious in your variable names: all the
INIT-CMDS share the same name space and may overwrite each other
in unpredictable ways. Sorry...
All these macros can be called multiple times, with different TAG
values, of course!
File: autoconf.info, Node: Configuration Files, Next: Makefile Substitutions, Prev: Configuration Actions, Up: Setup
4.7 Creating Configuration Files
================================
Be sure to read the previous section, *note Configuration Actions::.
-- Macro: AC_CONFIG_FILES (FILE..., [CMDS], [INIT-CMDS])
Make `AC_OUTPUT' create each `FILE' by copying an input file (by
default `FILE.in'), substituting the output variable values. This
macro is one of the instantiating macros; see *note Configuration
Actions::. *Note Makefile Substitutions::, for more information
on using output variables. *Note Setting Output Variables::, for
more information on creating them. This macro creates the
directory that the file is in if it doesn't exist. Usually,
makefiles are created this way, but other files, such as
`.gdbinit', can be specified as well.
Typical calls to `AC_CONFIG_FILES' look like this:
AC_CONFIG_FILES([Makefile src/Makefile man/Makefile X/Imakefile])
AC_CONFIG_FILES([autoconf], [chmod +x autoconf])
You can override an input file name by appending to FILE a
colon-separated list of input files. Examples:
AC_CONFIG_FILES([Makefile:boiler/top.mk:boiler/bot.mk]
[lib/Makefile:boiler/lib.mk])
Doing this allows you to keep your file names acceptable to DOS
variants, or to prepend and/or append boilerplate to the file.
File: autoconf.info, Node: Makefile Substitutions, Next: Configuration Headers, Prev: Configuration Files, Up: Setup
4.8 Substitutions in Makefiles
==============================
Each subdirectory in a distribution that contains something to be
compiled or installed should come with a file `Makefile.in', from which
`configure' creates a file `Makefile' in that directory. To create
`Makefile', `configure' performs a simple variable substitution,
replacing occurrences of `@VARIABLE@' in `Makefile.in' with the value
that `configure' has determined for that variable. Variables that are
substituted into output files in this way are called "output
variables". They are ordinary shell variables that are set in
`configure'. To make `configure' substitute a particular variable into
the output files, the macro `AC_SUBST' must be called with that
variable name as an argument. Any occurrences of `@VARIABLE@' for
other variables are left unchanged. *Note Setting Output Variables::,
for more information on creating output variables with `AC_SUBST'.
A software package that uses a `configure' script should be
distributed with a file `Makefile.in', but no makefile; that way, the
user has to properly configure the package for the local system before
compiling it.
*Note Makefile Conventions: (standards)Makefile Conventions, for
more information on what to put in makefiles.
* Menu:
* Preset Output Variables:: Output variables that are always set
* Installation Directory Variables:: Other preset output variables
* Changed Directory Variables:: Warnings about `datarootdir'
* Build Directories:: Supporting multiple concurrent compiles
* Automatic Remaking:: Makefile rules for configuring
File: autoconf.info, Node: Preset Output Variables, Next: Installation Directory Variables, Up: Makefile Substitutions
4.8.1 Preset Output Variables
-----------------------------
Some output variables are preset by the Autoconf macros. Some of the
Autoconf macros set additional output variables, which are mentioned in
the descriptions for those macros. *Note Output Variable Index::, for a
complete list of output variables. *Note Installation Directory
Variables::, for the list of the preset ones related to installation
directories. Below are listed the other preset ones, many of which are
precious variables (*note Setting Output Variables::, `AC_ARG_VAR').
The preset variables which are available during `config.status'
(*note Configuration Actions::) may also be used during `configure'
tests. For example, it is permissible to reference `$srcdir' when
constructing a list of directories to pass via option `-I' during a
compiler feature check. When used in this manner, coupled with the
fact that `configure' is always run from the top build directory, it is
sufficient to use just `$srcdir' instead of `$top_srcdir'.
-- Variable: CFLAGS
Debugging and optimization options for the C compiler. If it is
not set in the environment when `configure' runs, the default
value is set when you call `AC_PROG_CC' (or empty if you don't).
`configure' uses this variable when compiling or linking programs
to test for C features.
If a compiler option affects only the behavior of the preprocessor
(e.g., `-DNAME'), it should be put into `CPPFLAGS' instead. If it
affects only the linker (e.g., `-LDIRECTORY'), it should be put
into `LDFLAGS' instead. If it affects only the compiler proper,
`CFLAGS' is the natural home for it. If an option affects
multiple phases of the compiler, though, matters get tricky. One
approach to put such options directly into `CC', e.g., `CC='gcc
-m64''. Another is to put them into both `CPPFLAGS' and
`LDFLAGS', but not into `CFLAGS'.
However, remember that some `Makefile' variables are reserved by
the GNU Coding Standards for the use of the "user"--the person
building the package. For instance, `CFLAGS' is one such variable.
Sometimes package developers are tempted to set user variables
such as `CFLAGS' because it appears to make their job easier.
However, the package itself should never set a user variable,
particularly not to include switches that are required for proper
compilation of the package. Since these variables are documented
as being for the package builder, that person rightfully expects
to be able to override any of these variables at build time. If
the package developer needs to add switches without interfering
with the user, the proper way to do that is to introduce an
additional variable. Automake makes this easy by introducing
`AM_CFLAGS' (*note Flag Variables Ordering: (automake)Flag
Variables Ordering.), but the concept is the same even if Automake
is not used.
-- Variable: configure_input
A comment saying that the file was generated automatically by
`configure' and giving the name of the input file. `AC_OUTPUT'
adds a comment line containing this variable to the top of every
makefile it creates. For other files, you should reference this
variable in a comment at the top of each input file. For example,
an input shell script should begin like this:
#!/bin/sh
# @configure_input@
The presence of that line also reminds people editing the file
that it needs to be processed by `configure' in order to be used.
-- Variable: CPPFLAGS
Preprocessor options for the C, C++, Objective C, and Objective C++
preprocessors and compilers. If it is not set in the environment
when `configure' runs, the default value is empty. `configure'
uses this variable when preprocessing or compiling programs to
test for C, C++, Objective C, and Objective C++ features.
This variable's contents should contain options like `-I', `-D',
and `-U' that affect only the behavior of the preprocessor.
Please see the explanation of `CFLAGS' for what you can do if an
option affects other phases of the compiler as well.
Currently, `configure' always links as part of a single invocation
of the compiler that also preprocesses and compiles, so it uses
this variable also when linking programs. However, it is unwise to
depend on this behavior because the GNU Coding Standards do not
require it and many packages do not use `CPPFLAGS' when linking
programs.
*Note Special Chars in Variables::, for limitations that `CPPFLAGS'
might run into.
-- Variable: CXXFLAGS
Debugging and optimization options for the C++ compiler. It acts
like `CFLAGS', but for C++ instead of C.
-- Variable: DEFS
`-D' options to pass to the C compiler. If `AC_CONFIG_HEADERS' is
called, `configure' replaces `@DEFS@' with `-DHAVE_CONFIG_H'
instead (*note Configuration Headers::). This variable is not
defined while `configure' is performing its tests, only when
creating the output files. *Note Setting Output Variables::, for
how to check the results of previous tests.
-- Variable: ECHO_C
-- Variable: ECHO_N
-- Variable: ECHO_T
How does one suppress the trailing newline from `echo' for
question-answer message pairs? These variables provide a way:
echo $ECHO_N "And the winner is... $ECHO_C"
sleep 100000000000
echo "${ECHO_T}dead."
Some old and uncommon `echo' implementations offer no means to
achieve this, in which case `ECHO_T' is set to tab. You might not
want to use it.
-- Variable: ERLCFLAGS
Debugging and optimization options for the Erlang compiler. If it
is not set in the environment when `configure' runs, the default
value is empty. `configure' uses this variable when compiling
programs to test for Erlang features.
-- Variable: FCFLAGS
Debugging and optimization options for the Fortran compiler. If it
is not set in the environment when `configure' runs, the default
value is set when you call `AC_PROG_FC' (or empty if you don't).
`configure' uses this variable when compiling or linking programs
to test for Fortran features.
-- Variable: FFLAGS
Debugging and optimization options for the Fortran 77 compiler.
If it is not set in the environment when `configure' runs, the
default value is set when you call `AC_PROG_F77' (or empty if you
don't). `configure' uses this variable when compiling or linking
programs to test for Fortran 77 features.
-- Variable: LDFLAGS
Options for the linker. If it is not set in the environment when
`configure' runs, the default value is empty. `configure' uses
this variable when linking programs to test for C, C++, Objective
C, Objective C++, Fortran, and Go features.
This variable's contents should contain options like `-s' and `-L'
that affect only the behavior of the linker. Please see the
explanation of `CFLAGS' for what you can do if an option also
affects other phases of the compiler.
Don't use this variable to pass library names (`-l') to the
linker; use `LIBS' instead.
-- Variable: LIBS
`-l' options to pass to the linker. The default value is empty,
but some Autoconf macros may prepend extra libraries to this
variable if those libraries are found and provide necessary
functions, see *note Libraries::. `configure' uses this variable
when linking programs to test for C, C++, Objective C, Objective
C++, Fortran, and Go features.
-- Variable: OBJCFLAGS
Debugging and optimization options for the Objective C compiler.
It acts like `CFLAGS', but for Objective C instead of C.
-- Variable: OBJCXXFLAGS
Debugging and optimization options for the Objective C++ compiler.
It acts like `CXXFLAGS', but for Objective C++ instead of C++.
-- Variable: GOFLAGS
Debugging and optimization options for the Go compiler. It acts
like `CFLAGS', but for Go instead of C.
-- Variable: builddir
Rigorously equal to `.'. Added for symmetry only.
-- Variable: abs_builddir
Absolute name of `builddir'.
-- Variable: top_builddir
The relative name of the top level of the current build tree. In
the top-level directory, this is the same as `builddir'.
-- Variable: top_build_prefix
The relative name of the top level of the current build tree with
final slash if nonempty. This is the same as `top_builddir',
except that it contains zero or more runs of `../', so it should
not be appended with a slash for concatenation. This helps for
`make' implementations that otherwise do not treat `./file' and
`file' as equal in the toplevel build directory.
-- Variable: abs_top_builddir
Absolute name of `top_builddir'.
-- Variable: srcdir
The name of the directory that contains the source code for that
makefile.
-- Variable: abs_srcdir
Absolute name of `srcdir'.
-- Variable: top_srcdir
The name of the top-level source code directory for the package.
In the top-level directory, this is the same as `srcdir'.
-- Variable: abs_top_srcdir
Absolute name of `top_srcdir'.
File: autoconf.info, Node: Installation Directory Variables, Next: Changed Directory Variables, Prev: Preset Output Variables, Up: Makefile Substitutions
4.8.2 Installation Directory Variables
--------------------------------------
The following variables specify the directories for package
installation, see *note Variables for Installation Directories:
(standards)Directory Variables, for more information. Each variable
corresponds to an argument of `configure'; trailing slashes are
stripped so that expressions such as `${prefix}/lib' expand with only
one slash between directory names. See the end of this section for
details on when and how to use these variables.
-- Variable: bindir
The directory for installing executables that users run.
-- Variable: datadir
The directory for installing idiosyncratic read-only
architecture-independent data.
-- Variable: datarootdir
The root of the directory tree for read-only
architecture-independent data files.
-- Variable: docdir
The directory for installing documentation files (other than Info
and man).
-- Variable: dvidir
The directory for installing documentation files in DVI format.
-- Variable: exec_prefix
The installation prefix for architecture-dependent files. By
default it's the same as `prefix'. You should avoid installing
anything directly to `exec_prefix'. However, the default value for
directories containing architecture-dependent files should be
relative to `exec_prefix'.
-- Variable: htmldir
The directory for installing HTML documentation.
-- Variable: includedir
The directory for installing C header files.
-- Variable: infodir
The directory for installing documentation in Info format.
-- Variable: libdir
The directory for installing object code libraries.
-- Variable: libexecdir
The directory for installing executables that other programs run.
-- Variable: localedir
The directory for installing locale-dependent but
architecture-independent data, such as message catalogs. This
directory usually has a subdirectory per locale.
-- Variable: localstatedir
The directory for installing modifiable single-machine data.
-- Variable: mandir
The top-level directory for installing documentation in man format.
-- Variable: oldincludedir
The directory for installing C header files for non-GCC compilers.
-- Variable: pdfdir
The directory for installing PDF documentation.
-- Variable: prefix
The common installation prefix for all files. If `exec_prefix' is
defined to a different value, `prefix' is used only for
architecture-independent files.
-- Variable: psdir
The directory for installing PostScript documentation.
-- Variable: sbindir
The directory for installing executables that system
administrators run.
-- Variable: sharedstatedir
The directory for installing modifiable architecture-independent
data.
-- Variable: sysconfdir
The directory for installing read-only single-machine data.
Most of these variables have values that rely on `prefix' or
`exec_prefix'. It is deliberate that the directory output variables
keep them unexpanded: typically `@datarootdir@' is replaced by
`${prefix}/share', not `/usr/local/share', and `@datadir@' is replaced
by `${datarootdir}'.
This behavior is mandated by the GNU Coding Standards, so that when
the user runs:
`make'
she can still specify a different prefix from the one specified to
`configure', in which case, if needed, the package should hard
code dependencies corresponding to the make-specified prefix.
`make install'
she can specify a different installation location, in which case
the package _must_ still depend on the location which was compiled
in (i.e., never recompile when `make install' is run). This is an
extremely important feature, as many people may decide to install
all the files of a package grouped together, and then install
links from the final locations to there.
In order to support these features, it is essential that
`datarootdir' remains defined as `${prefix}/share', so that its value
can be expanded based on the current value of `prefix'.
A corollary is that you should not use these variables except in
makefiles. For instance, instead of trying to evaluate `datadir' in
`configure' and hard-coding it in makefiles using e.g.,
`AC_DEFINE_UNQUOTED([DATADIR], ["$datadir"], [Data directory.])', you
should add `-DDATADIR='$(datadir)'' to your makefile's definition of
`CPPFLAGS' (`AM_CPPFLAGS' if you are also using Automake).
Similarly, you should not rely on `AC_CONFIG_FILES' to replace
`bindir' and friends in your shell scripts and other files; instead,
let `make' manage their replacement. For instance Autoconf ships
templates of its shell scripts ending with `.in', and uses a makefile
snippet similar to the following to build scripts like `autoheader' and
`autom4te':
edit = sed \
-e 's|@bindir[@]|$(bindir)|g' \
-e 's|@pkgdatadir[@]|$(pkgdatadir)|g' \
-e 's|@prefix[@]|$(prefix)|g'
autoheader autom4te: Makefile
rm -f $@ $@.tmp
srcdir=''; \
test -f ./$@.in || srcdir=$(srcdir)/; \
$(edit) $${srcdir}$@.in >$@.tmp
chmod +x $@.tmp
chmod a-w $@.tmp
mv $@.tmp $@
autoheader: $(srcdir)/autoheader.in
autom4te: $(srcdir)/autom4te.in
Some details are noteworthy:
`@bindir[@]'
The brackets prevent `configure' from replacing `@bindir@' in the
Sed expression itself. Brackets are preferable to a backslash
here, since Posix says `\@' is not portable.
`$(bindir)'
Don't use `@bindir@'! Use the matching makefile variable instead.
`$(pkgdatadir)'
The example takes advantage of the variable `$(pkgdatadir)'
provided by Automake; it is equivalent to `$(datadir)/$(PACKAGE)'.
`/'
Don't use `/' in the Sed expressions that replace file names since
most likely the variables you use, such as `$(bindir)', contain
`/'. Use a shell metacharacter instead, such as `|'.
special characters
File names, file name components, and the value of `VPATH' should
not contain shell metacharacters or white space. *Note Special
Chars in Variables::.
dependency on `Makefile'
Since `edit' uses values that depend on the configuration specific
values (`prefix', etc.) and not only on `VERSION' and so forth,
the output depends on `Makefile', not `configure.ac'.
`$@'
The main rule is generic, and uses `$@' extensively to avoid the
need for multiple copies of the rule.
Separated dependencies and single suffix rules
You can't use them! The above snippet cannot be (portably)
rewritten as:
autoconf autoheader: Makefile
.in:
rm -f $@ $@.tmp
$(edit) $< >$@.tmp
chmod +x $@.tmp
mv $@.tmp $@
*Note Single Suffix Rules::, for details.
`$(srcdir)'
Be sure to specify the name of the source directory, otherwise the
package won't support separated builds.
For the more specific installation of Erlang libraries, the
following variables are defined:
-- Variable: ERLANG_INSTALL_LIB_DIR
The common parent directory of Erlang library installation
directories. This variable is set by calling the
`AC_ERLANG_SUBST_INSTALL_LIB_DIR' macro in `configure.ac'.
-- Variable: ERLANG_INSTALL_LIB_DIR_LIBRARY
The installation directory for Erlang library LIBRARY. This
variable is set by using the `AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR'
macro in `configure.ac'.
*Note Erlang Libraries::, for details.
File: autoconf.info, Node: Changed Directory Variables, Next: Build Directories, Prev: Installation Directory Variables, Up: Makefile Substitutions
4.8.3 Changed Directory Variables
---------------------------------
In Autoconf 2.60, the set of directory variables has changed, and the
defaults of some variables have been adjusted (*note Installation
Directory Variables::) to changes in the GNU Coding Standards.
Notably, `datadir', `infodir', and `mandir' are now expressed in terms
of `datarootdir'. If you are upgrading from an earlier Autoconf
version, you may need to adjust your files to ensure that the directory
variables are substituted correctly (*note Defining Directories::), and
that a definition of `datarootdir' is in place. For example, in a
`Makefile.in', adding
datarootdir = @datarootdir@
is usually sufficient. If you use Automake to create `Makefile.in', it
will add this for you.
To help with the transition, Autoconf warns about files that seem to
use `datarootdir' without defining it. In some cases, it then expands
the value of `$datarootdir' in substitutions of the directory
variables. The following example shows such a warning:
$ cat configure.ac
AC_INIT
AC_CONFIG_FILES([Makefile])
AC_OUTPUT
$ cat Makefile.in
prefix = @prefix@
datadir = @datadir@
$ autoconf
$ configure
configure: creating ./config.status
config.status: creating Makefile
config.status: WARNING:
Makefile.in seems to ignore the --datarootdir setting
$ cat Makefile
prefix = /usr/local
datadir = ${prefix}/share
Usually one can easily change the file to accommodate both older and
newer Autoconf releases:
$ cat Makefile.in
prefix = @prefix@
datarootdir = @datarootdir@
datadir = @datadir@
$ configure
configure: creating ./config.status
config.status: creating Makefile
$ cat Makefile
prefix = /usr/local
datarootdir = ${prefix}/share
datadir = ${datarootdir}
In some cases, however, the checks may not be able to detect that a
suitable initialization of `datarootdir' is in place, or they may fail
to detect that such an initialization is necessary in the output file.
If, after auditing your package, there are still spurious `configure'
warnings about `datarootdir', you may add the line
AC_DEFUN([AC_DATAROOTDIR_CHECKED])
to your `configure.ac' to disable the warnings. This is an exception
to the usual rule that you should not define a macro whose name begins
with `AC_' (*note Macro Names::).
File: autoconf.info, Node: Build Directories, Next: Automatic Remaking, Prev: Changed Directory Variables, Up: Makefile Substitutions
4.8.4 Build Directories
-----------------------
You can support compiling a software package for several architectures
simultaneously from the same copy of the source code. The object files
for each architecture are kept in their own directory.
To support doing this, `make' uses the `VPATH' variable to find the
files that are in the source directory. GNU Make can do this. Most
other recent `make' programs can do this as well, though they may have
difficulties and it is often simpler to recommend GNU `make' (*note
VPATH and Make::). Older `make' programs do not support `VPATH'; when
using them, the source code must be in the same directory as the object
files.
If you are using GNU Automake, the remaining details in this section
are already covered for you, based on the contents of your
`Makefile.am'. But if you are using Autoconf in isolation, then
supporting `VPATH' requires the following in your `Makefile.in':
srcdir = @srcdir@
VPATH = @srcdir@
Do not set `VPATH' to the value of another variable (*note Variables
listed in VPATH::.
`configure' substitutes the correct value for `srcdir' when it
produces `Makefile'.
Do not use the `make' variable `$
File: autoconf.info, Node: Automatic Remaking, Prev: Build Directories, Up: Makefile Substitutions
4.8.5 Automatic Remaking
------------------------
You can put rules like the following in the top-level `Makefile.in' for
a package to automatically update the configuration information when
you change the configuration files. This example includes all of the
optional files, such as `aclocal.m4' and those related to configuration
header files. Omit from the `Makefile.in' rules for any of these files
that your package does not use.
The `$(srcdir)/' prefix is included because of limitations in the
`VPATH' mechanism.
The `stamp-' files are necessary because the timestamps of
`config.h.in' and `config.h' are not changed if remaking them does not
change their contents. This feature avoids unnecessary recompilation.
You should include the file `stamp-h.in' in your package's
distribution, so that `make' considers `config.h.in' up to date. Don't
use `touch' (*note Limitations of Usual Tools: touch.); instead, use
`echo' (using `date' would cause needless differences, hence CVS
conflicts, etc.).
$(srcdir)/configure: configure.ac aclocal.m4
cd '$(srcdir)' && autoconf
# autoheader might not change config.h.in, so touch a stamp file.
$(srcdir)/config.h.in: stamp-h.in
$(srcdir)/stamp-h.in: configure.ac aclocal.m4
cd '$(srcdir)' && autoheader
echo timestamp > '$(srcdir)/stamp-h.in'
config.h: stamp-h
stamp-h: config.h.in config.status
./config.status
Makefile: Makefile.in config.status
./config.status
config.status: configure
./config.status --recheck
(Be careful if you copy these lines directly into your makefile, as you
need to convert the indented lines to start with the tab character.)
In addition, you should use
AC_CONFIG_FILES([stamp-h], [echo timestamp > stamp-h])
so `config.status' ensures that `config.h' is considered up to date.
*Note Output::, for more information about `AC_OUTPUT'.
*Note config.status Invocation::, for more examples of handling
configuration-related dependencies.
File: autoconf.info, Node: Configuration Headers, Next: Configuration Commands, Prev: Makefile Substitutions, Up: Setup
4.9 Configuration Header Files
==============================
When a package contains more than a few tests that define C preprocessor
symbols, the command lines to pass `-D' options to the compiler can get
quite long. This causes two problems. One is that the `make' output
is hard to visually scan for errors. More seriously, the command lines
can exceed the length limits of some operating systems. As an
alternative to passing `-D' options to the compiler, `configure'
scripts can create a C header file containing `#define' directives.
The `AC_CONFIG_HEADERS' macro selects this kind of output. Though it
can be called anywhere between `AC_INIT' and `AC_OUTPUT', it is
customary to call it right after `AC_INIT'.
The package should `#include' the configuration header file before
any other header files, to prevent inconsistencies in declarations (for
example, if it redefines `const').
To provide for VPATH builds, remember to pass the C compiler a `-I.'
option (or `-I..'; whichever directory contains `config.h'). Even if
you use `#include "config.h"', the preprocessor searches only the
directory of the currently read file, i.e., the source directory, not
the build directory.
With the appropriate `-I' option, you can use `#include '.
Actually, it's a good habit to use it, because in the rare case when
the source directory contains another `config.h', the build directory
should be searched first.
-- Macro: AC_CONFIG_HEADERS (HEADER ..., [CMDS], [INIT-CMDS])
This macro is one of the instantiating macros; see *note
Configuration Actions::. Make `AC_OUTPUT' create the file(s) in
the blank-or-newline-separated list HEADER containing C
preprocessor `#define' statements, and replace `@DEFS@' in
generated files with `-DHAVE_CONFIG_H' instead of the value of
`DEFS'. The usual name for HEADER is `config.h'.
If HEADER already exists and its contents are identical to what
`AC_OUTPUT' would put in it, it is left alone. Doing this allows
making some changes in the configuration without needlessly causing
object files that depend on the header file to be recompiled.
Usually the input file is named `HEADER.in'; however, you can
override the input file name by appending to HEADER a
colon-separated list of input files. For example, you might need
to make the input file name acceptable to DOS variants:
AC_CONFIG_HEADERS([config.h:config.hin])
-- Macro: AH_HEADER
This macro is defined as the name of the first declared config
header and undefined if no config headers have been declared up to
this point. A third-party macro may, for example, require use of
a config header without invoking AC_CONFIG_HEADERS twice, like
this:
AC_CONFIG_COMMANDS_PRE(
[m4_ifndef([AH_HEADER], [AC_CONFIG_HEADERS([config.h])])])
*Note Configuration Actions::, for more details on HEADER.
* Menu:
* Header Templates:: Input for the configuration headers
* autoheader Invocation:: How to create configuration templates
* Autoheader Macros:: How to specify CPP templates
File: autoconf.info, Node: Header Templates, Next: autoheader Invocation, Up: Configuration Headers
4.9.1 Configuration Header Templates
------------------------------------
Your distribution should contain a template file that looks as you want
the final header file to look, including comments, with `#undef'
statements which are used as hooks. For example, suppose your
`configure.ac' makes these calls:
AC_CONFIG_HEADERS([conf.h])
AC_CHECK_HEADERS([unistd.h])
Then you could have code like the following in `conf.h.in'. The
`conf.h' created by `configure' defines `HAVE_UNISTD_H' to 1, if and
only if the system has `unistd.h'.
/* Define as 1 if you have unistd.h. */
#undef HAVE_UNISTD_H
The format of the template file is stricter than what the C
preprocessor is required to accept. A directive line should contain
only whitespace, `#undef', and `HAVE_UNISTD_H'. The use of `#define'
instead of `#undef', or of comments on the same line as `#undef', is
strongly discouraged. Each hook should only be listed once. Other
preprocessor lines, such as `#ifdef' or `#include', are copied verbatim
from the template into the generated header.
Since it is a tedious task to keep a template header up to date, you
may use `autoheader' to generate it, see *note autoheader Invocation::.
During the instantiation of the header, each `#undef' line in the
template file for each symbol defined by `AC_DEFINE' is changed to an
appropriate `#define'. If the corresponding `AC_DEFINE' has not been
executed during the `configure' run, the `#undef' line is commented
out. (This is important, e.g., for `_POSIX_SOURCE': on many systems,
it can be implicitly defined by the compiler, and undefining it in the
header would then break compilation of subsequent headers.)
Currently, _all_ remaining `#undef' lines in the header template are
commented out, whether or not there was a corresponding `AC_DEFINE' for
the macro name; but this behavior is not guaranteed for future releases
of Autoconf.
Generally speaking, since you should not use `#define', and you
cannot guarantee whether a `#undef' directive in the header template
will be converted to a `#define' or commented out in the generated
header file, the template file cannot be used for conditional
definition effects. Consequently, if you need to use the construct
#ifdef THIS
# define THAT
#endif
you must place it outside of the template. If you absolutely need to
hook it to the config header itself, please put the directives to a
separate file, and `#include' that file from the config header
template. If you are using `autoheader', you would probably use
`AH_BOTTOM' to append the `#include' directive.
File: autoconf.info, Node: autoheader Invocation, Next: Autoheader Macros, Prev: Header Templates, Up: Configuration Headers
4.9.2 Using `autoheader' to Create `config.h.in'
------------------------------------------------
The `autoheader' program can create a template file of C `#define'
statements for `configure' to use. It searches for the first
invocation of `AC_CONFIG_HEADERS' in `configure' sources to determine
the name of the template. (If the first call of `AC_CONFIG_HEADERS'
specifies more than one input file name, `autoheader' uses the first
one.)
It is recommended that only one input file is used. If you want to
append a boilerplate code, it is preferable to use `AH_BOTTOM([#include
])'. File `conf_post.h' is not processed during the
configuration then, which make things clearer. Analogically, `AH_TOP'
can be used to prepend a boilerplate code.
In order to do its job, `autoheader' needs you to document all of
the symbols that you might use. Typically this is done via an
`AC_DEFINE' or `AC_DEFINE_UNQUOTED' call whose first argument is a
literal symbol and whose third argument describes the symbol (*note
Defining Symbols::). Alternatively, you can use `AH_TEMPLATE' (*note
Autoheader Macros::), or you can supply a suitable input file for a
subsequent configuration header file. Symbols defined by Autoconf's
builtin tests are already documented properly; you need to document
only those that you define yourself.
You might wonder why `autoheader' is needed: after all, why would
`configure' need to "patch" a `config.h.in' to produce a `config.h'
instead of just creating `config.h' from scratch? Well, when
everything rocks, the answer is just that we are wasting our time
maintaining `autoheader': generating `config.h' directly is all that is
needed. When things go wrong, however, you'll be thankful for the
existence of `autoheader'.
The fact that the symbols are documented is important in order to
_check_ that `config.h' makes sense. The fact that there is a
well-defined list of symbols that should be defined (or not) is also
important for people who are porting packages to environments where
`configure' cannot be run: they just have to _fill in the blanks_.
But let's come back to the point: the invocation of `autoheader'...
If you give `autoheader' an argument, it uses that file instead of
`configure.ac' and writes the header file to the standard output
instead of to `config.h.in'. If you give `autoheader' an argument of
`-', it reads the standard input instead of `configure.ac' and writes
the header file to the standard output.
`autoheader' accepts the following options:
`--help'
`-h'
Print a summary of the command line options and exit.
`--version'
`-V'
Print the version number of Autoconf and exit.
`--verbose'
`-v'
Report processing steps.
`--debug'
`-d'
Don't remove the temporary files.
`--force'
`-f'
Remake the template file even if newer than its input files.
`--include=DIR'
`-I DIR'
Append DIR to the include path. Multiple invocations accumulate.
`--prepend-include=DIR'
`-B DIR'
Prepend DIR to the include path. Multiple invocations accumulate.
`--warnings=CATEGORY'
`-W CATEGORY'
Report the warnings related to CATEGORY (which can actually be a
comma separated list). Current categories include:
`obsolete'
report the uses of obsolete constructs
`all'
report all the warnings
`none'
report none
`error'
treats warnings as errors
`no-CATEGORY'
disable warnings falling into CATEGORY
File: autoconf.info, Node: Autoheader Macros, Prev: autoheader Invocation, Up: Configuration Headers
4.9.3 Autoheader Macros
-----------------------
`autoheader' scans `configure.ac' and figures out which C preprocessor
symbols it might define. It knows how to generate templates for
symbols defined by `AC_CHECK_HEADERS', `AC_CHECK_FUNCS' etc., but if
you `AC_DEFINE' any additional symbol, you must define a template for
it. If there are missing templates, `autoheader' fails with an error
message.
The template for a SYMBOL is created by `autoheader' from the
DESCRIPTION argument to an `AC_DEFINE'; see *note Defining Symbols::.
For special needs, you can use the following macros.
-- Macro: AH_TEMPLATE (KEY, DESCRIPTION)
Tell `autoheader' to generate a template for KEY. This macro
generates standard templates just like `AC_DEFINE' when a
DESCRIPTION is given.
For example:
AH_TEMPLATE([CRAY_STACKSEG_END],
[Define to one of _getb67, GETB67, getb67
for Cray-2 and Cray-YMP systems. This
function is required for alloca.c support
on those systems.])
generates the following template, with the description properly
justified.
/* Define to one of _getb67, GETB67, getb67 for Cray-2 and
Cray-YMP systems. This function is required for alloca.c
support on those systems. */
#undef CRAY_STACKSEG_END
-- Macro: AH_VERBATIM (KEY, TEMPLATE)
Tell `autoheader' to include the TEMPLATE as-is in the header
template file. This TEMPLATE is associated with the KEY, which is
used to sort all the different templates and guarantee their
uniqueness. It should be a symbol that can be defined via
`AC_DEFINE'.
-- Macro: AH_TOP (TEXT)
Include TEXT at the top of the header template file.
-- Macro: AH_BOTTOM (TEXT)
Include TEXT at the bottom of the header template file.
Please note that TEXT gets included "verbatim" to the template file,
not to the resulting config header, so it can easily get mangled when
the template is processed. There is rarely a need for something other
than
AH_BOTTOM([#include ])
File: autoconf.info, Node: Configuration Commands, Next: Configuration Links, Prev: Configuration Headers, Up: Setup
4.10 Running Arbitrary Configuration Commands
=============================================
You can execute arbitrary commands before, during, and after
`config.status' is run. The three following macros accumulate the
commands to run when they are called multiple times.
`AC_CONFIG_COMMANDS' replaces the obsolete macro `AC_OUTPUT_COMMANDS';
see *note Obsolete Macros::, for details.
-- Macro: AC_CONFIG_COMMANDS (TAG..., [CMDS], [INIT-CMDS])
Specify additional shell commands to run at the end of
`config.status', and shell commands to initialize any variables
from `configure'. Associate the commands with TAG. Since
typically the CMDS create a file, TAG should naturally be the name
of that file. If needed, the directory hosting TAG is created.
This macro is one of the instantiating macros; see *note
Configuration Actions::.
Here is an unrealistic example:
fubar=42
AC_CONFIG_COMMANDS([fubar],
[echo this is extra $fubar, and so on.],
[fubar=$fubar])
Here is a better one:
AC_CONFIG_COMMANDS([timestamp], [date >timestamp])
The following two macros look similar, but in fact they are not of
the same breed: they are executed directly by `configure', so you
cannot use `config.status' to rerun them.
-- Macro: AC_CONFIG_COMMANDS_PRE (CMDS)
Execute the CMDS right before creating `config.status'.
This macro presents the last opportunity to call `AC_SUBST',
`AC_DEFINE', or `AC_CONFIG_ITEMS' macros.
-- Macro: AC_CONFIG_COMMANDS_POST (CMDS)
Execute the CMDS right after creating `config.status'.
File: autoconf.info, Node: Configuration Links, Next: Subdirectories, Prev: Configuration Commands, Up: Setup
4.11 Creating Configuration Links
=================================
You may find it convenient to create links whose destinations depend
upon results of tests. One can use `AC_CONFIG_COMMANDS' but the
creation of relative symbolic links can be delicate when the package is
built in a directory different from the source directory.
-- Macro: AC_CONFIG_LINKS (DEST:SOURCE..., [CMDS], [INIT-CMDS])
Make `AC_OUTPUT' link each of the existing files SOURCE to the
corresponding link name DEST. Makes a symbolic link if possible,
otherwise a hard link if possible, otherwise a copy. The DEST and
SOURCE names should be relative to the top level source or build
directory. This macro is one of the instantiating macros; see
*note Configuration Actions::.
For example, this call:
AC_CONFIG_LINKS([host.h:config/$machine.h
object.h:config/$obj_format.h])
creates in the current directory `host.h' as a link to
`SRCDIR/config/$machine.h', and `object.h' as a link to
`SRCDIR/config/$obj_format.h'.
The tempting value `.' for DEST is invalid: it makes it impossible
for `config.status' to guess the links to establish.
One can then run:
./config.status host.h object.h
to create the links.
File: autoconf.info, Node: Subdirectories, Next: Default Prefix, Prev: Configuration Links, Up: Setup
4.12 Configuring Other Packages in Subdirectories
=================================================
In most situations, calling `AC_OUTPUT' is sufficient to produce
makefiles in subdirectories. However, `configure' scripts that control
more than one independent package can use `AC_CONFIG_SUBDIRS' to run
`configure' scripts for other packages in subdirectories.
-- Macro: AC_CONFIG_SUBDIRS (DIR ...)
Make `AC_OUTPUT' run `configure' in each subdirectory DIR in the
given blank-or-newline-separated list. Each DIR should be a
literal, i.e., please do not use:
if test "x$package_foo_enabled" = xyes; then
my_subdirs="$my_subdirs foo"
fi
AC_CONFIG_SUBDIRS([$my_subdirs])
because this prevents `./configure --help=recursive' from
displaying the options of the package `foo'. Instead, you should
write:
if test "x$package_foo_enabled" = xyes; then
AC_CONFIG_SUBDIRS([foo])
fi
If a given DIR is not found at `configure' run time, a warning is
reported; if the subdirectory is optional, write:
if test -d "$srcdir/foo"; then
AC_CONFIG_SUBDIRS([foo])
fi
If a given DIR contains `configure.gnu', it is run instead of
`configure'. This is for packages that might use a non-Autoconf
script `Configure', which can't be called through a wrapper
`configure' since it would be the same file on case-insensitive
file systems. Likewise, if a DIR contains `configure.in' but no
`configure', the Cygnus `configure' script found by
`AC_CONFIG_AUX_DIR' is used.
The subdirectory `configure' scripts are given the same command
line options that were given to this `configure' script, with minor
changes if needed, which include:
- adjusting a relative name for the cache file;
- adjusting a relative name for the source directory;
- propagating the current value of `$prefix', including if it
was defaulted, and if the default values of the top level and
of the subdirectory `configure' differ.
This macro also sets the output variable `subdirs' to the list of
directories `DIR ...'. Make rules can use this variable to
determine which subdirectories to recurse into.
This macro may be called multiple times.
File: autoconf.info, Node: Default Prefix, Prev: Subdirectories, Up: Setup
4.13 Default Prefix
===================
By default, `configure' sets the prefix for files it installs to
`/usr/local'. The user of `configure' can select a different prefix
using the `--prefix' and `--exec-prefix' options. There are two ways
to change the default: when creating `configure', and when running it.
Some software packages might want to install in a directory other
than `/usr/local' by default. To accomplish that, use the
`AC_PREFIX_DEFAULT' macro.
-- Macro: AC_PREFIX_DEFAULT (PREFIX)
Set the default installation prefix to PREFIX instead of
`/usr/local'.
It may be convenient for users to have `configure' guess the
installation prefix from the location of a related program that they
have already installed. If you wish to do that, you can call
`AC_PREFIX_PROGRAM'.
-- Macro: AC_PREFIX_PROGRAM (PROGRAM)
If the user did not specify an installation prefix (using the
`--prefix' option), guess a value for it by looking for PROGRAM in
`PATH', the way the shell does. If PROGRAM is found, set the
prefix to the parent of the directory containing PROGRAM, else
default the prefix as described above (`/usr/local' or
`AC_PREFIX_DEFAULT'). For example, if PROGRAM is `gcc' and the
`PATH' contains `/usr/local/gnu/bin/gcc', set the prefix to
`/usr/local/gnu'.
File: autoconf.info, Node: Existing Tests, Next: Writing Tests, Prev: Setup, Up: Top
5 Existing Tests
****************
These macros test for particular system features that packages might
need or want to use. If you need to test for a kind of feature that
none of these macros check for, you can probably do it by calling
primitive test macros with appropriate arguments (*note Writing
Tests::).
These tests print messages telling the user which feature they're
checking for, and what they find. They cache their results for future
`configure' runs (*note Caching Results::).
Some of these macros set output variables. *Note Makefile
Substitutions::, for how to get their values. The phrase "define NAME"
is used below as a shorthand to mean "define the C preprocessor symbol
NAME to the value 1". *Note Defining Symbols::, for how to get those
symbol definitions into your program.
* Menu:
* Common Behavior:: Macros' standard schemes
* Alternative Programs:: Selecting between alternative programs
* Files:: Checking for the existence of files
* Libraries:: Library archives that might be missing
* Library Functions:: C library functions that might be missing
* Header Files:: Header files that might be missing
* Declarations:: Declarations that may be missing
* Structures:: Structures or members that might be missing
* Types:: Types that might be missing
* Compilers and Preprocessors:: Checking for compiling programs
* System Services:: Operating system services
* Posix Variants:: Special kludges for specific Posix variants
* Erlang Libraries:: Checking for the existence of Erlang libraries
File: autoconf.info, Node: Common Behavior, Next: Alternative Programs, Up: Existing Tests
5.1 Common Behavior
===================
Much effort has been expended to make Autoconf easy to learn. The most
obvious way to reach this goal is simply to enforce standard interfaces
and behaviors, avoiding exceptions as much as possible. Because of
history and inertia, unfortunately, there are still too many exceptions
in Autoconf; nevertheless, this section describes some of the common
rules.
* Menu:
* Standard Symbols:: Symbols defined by the macros
* Default Includes:: Includes used by the generic macros
File: autoconf.info, Node: Standard Symbols, Next: Default Includes, Up: Common Behavior
5.1.1 Standard Symbols
----------------------
All the generic macros that `AC_DEFINE' a symbol as a result of their
test transform their ARGUMENT values to a standard alphabet. First,
ARGUMENT is converted to upper case and any asterisks (`*') are each
converted to `P'. Any remaining characters that are not alphanumeric
are converted to underscores.
For instance,
AC_CHECK_TYPES([struct $Expensive*])
defines the symbol `HAVE_STRUCT__EXPENSIVEP' if the check succeeds.
File: autoconf.info, Node: Default Includes, Prev: Standard Symbols, Up: Common Behavior
5.1.2 Default Includes
----------------------
Several tests depend upon a set of header files. Since these headers
are not universally available, tests actually have to provide a set of
protected includes, such as:
#ifdef TIME_WITH_SYS_TIME
# include
# include
#else
# ifdef HAVE_SYS_TIME_H
# include
# else
# include
# endif
#endif
Unless you know exactly what you are doing, you should avoid using
unconditional includes, and check the existence of the headers you
include beforehand (*note Header Files::).
Most generic macros use the following macro to provide the default
set of includes:
-- Macro: AC_INCLUDES_DEFAULT ([INCLUDE-DIRECTIVES])
Expand to INCLUDE-DIRECTIVES if defined, otherwise to:
#include
#ifdef HAVE_SYS_TYPES_H
# include
#endif
#ifdef HAVE_SYS_STAT_H
# include
#endif
#ifdef STDC_HEADERS
# include
# include
#else
# ifdef HAVE_STDLIB_H
# include
# endif
#endif
#ifdef HAVE_STRING_H
# if !defined STDC_HEADERS && defined HAVE_MEMORY_H
# include
# endif
# include
#endif
#ifdef HAVE_STRINGS_H
# include
#endif
#ifdef HAVE_INTTYPES_H
# include
#endif
#ifdef HAVE_STDINT_H
# include
#endif
#ifdef HAVE_UNISTD_H
# include
#endif
If the default includes are used, then check for the presence of
these headers and their compatibility, i.e., you don't need to run
`AC_HEADER_STDC', nor check for `stdlib.h' etc.
These headers are checked for in the same order as they are
included. For instance, on some systems `string.h' and
`strings.h' both exist, but conflict. Then `HAVE_STRING_H' is
defined, not `HAVE_STRINGS_H'.
File: autoconf.info, Node: Alternative Programs, Next: Files, Prev: Common Behavior, Up: Existing Tests
5.2 Alternative Programs
========================
These macros check for the presence or behavior of particular programs.
They are used to choose between several alternative programs and to
decide what to do once one has been chosen. If there is no macro
specifically defined to check for a program you need, and you don't need
to check for any special properties of it, then you can use one of the
general program-check macros.
* Menu:
* Particular Programs:: Special handling to find certain programs
* Generic Programs:: How to find other programs
File: autoconf.info, Node: Particular Programs, Next: Generic Programs, Up: Alternative Programs
5.2.1 Particular Program Checks
-------------------------------
These macros check for particular programs--whether they exist, and in
some cases whether they support certain features.
-- Macro: AC_PROG_AWK
Check for `gawk', `mawk', `nawk', and `awk', in that order, and
set output variable `AWK' to the first one that is found. It
tries `gawk' first because that is reported to be the best
implementation. The result can be overridden by setting the
variable `AWK' or the cache variable `ac_cv_prog_AWK'.
Using this macro is sufficient to avoid the pitfalls of traditional
`awk' (*note Limitations of Usual Tools: awk.).
-- Macro: AC_PROG_GREP
Look for the best available `grep' or `ggrep' that accepts the
longest input lines possible, and that supports multiple `-e'
options. Set the output variable `GREP' to whatever is chosen.
*Note Limitations of Usual Tools: grep, for more information about
portability problems with the `grep' command family. The result
can be overridden by setting the `GREP' variable and is cached in
the `ac_cv_path_GREP' variable.
-- Macro: AC_PROG_EGREP
Check whether `$GREP -E' works, or else look for the best available
`egrep' or `gegrep' that accepts the longest input lines possible.
Set the output variable `EGREP' to whatever is chosen. The result
can be overridden by setting the `EGREP' variable and is cached in
the `ac_cv_path_EGREP' variable.
-- Macro: AC_PROG_FGREP
Check whether `$GREP -F' works, or else look for the best available
`fgrep' or `gfgrep' that accepts the longest input lines possible.
Set the output variable `FGREP' to whatever is chosen. The result
can be overridden by setting the `FGREP' variable and is cached in
the `ac_cv_path_FGREP' variable.
-- Macro: AC_PROG_INSTALL
Set output variable `INSTALL' to the name of a BSD-compatible
`install' program, if one is found in the current `PATH'.
Otherwise, set `INSTALL' to `DIR/install-sh -c', checking the
directories specified to `AC_CONFIG_AUX_DIR' (or its default
directories) to determine DIR (*note Output::). Also set the
variables `INSTALL_PROGRAM' and `INSTALL_SCRIPT' to `${INSTALL}'
and `INSTALL_DATA' to `${INSTALL} -m 644'.
`@INSTALL@' is special, as its value may vary for different
configuration files.
This macro screens out various instances of `install' known not to
work. It prefers to find a C program rather than a shell script,
for speed. Instead of `install-sh', it can also use `install.sh',
but that name is obsolete because some `make' programs have a rule
that creates `install' from it if there is no makefile. Further,
this macro requires `install' to be able to install multiple files
into a target directory in a single invocation.
Autoconf comes with a copy of `install-sh' that you can use. If
you use `AC_PROG_INSTALL', you must include either `install-sh' or
`install.sh' in your distribution; otherwise `configure' produces
an error message saying it can't find them--even if the system
you're on has a good `install' program. This check is a safety
measure to prevent you from accidentally leaving that file out,
which would prevent your package from installing on systems that
don't have a BSD-compatible `install' program.
If you need to use your own installation program because it has
features not found in standard `install' programs, there is no
reason to use `AC_PROG_INSTALL'; just put the file name of your
program into your `Makefile.in' files.
The result of the test can be overridden by setting the variable
`INSTALL' or the cache variable `ac_cv_path_install'.
-- Macro: AC_PROG_MKDIR_P
Set output variable `MKDIR_P' to a program that ensures that for
each argument, a directory named by this argument exists, creating
it and its parent directories if needed, and without race
conditions when two instances of the program attempt to make the
same directory at nearly the same time.
This macro uses the `mkdir -p' command if possible. Otherwise, it
falls back on invoking `install-sh' with the `-d' option, so your
package should contain `install-sh' as described under
`AC_PROG_INSTALL'. An `install-sh' file that predates Autoconf
2.60 or Automake 1.10 is vulnerable to race conditions, so if you
want to support parallel installs from different packages into the
same directory you need to make sure you have an up-to-date
`install-sh'. In particular, be careful about using `autoreconf
-if' if your Automake predates Automake 1.10.
This macro is related to the `AS_MKDIR_P' macro (*note Programming
in M4sh::), but it sets an output variable intended for use in
other files, whereas `AS_MKDIR_P' is intended for use in scripts
like `configure'. Also, `AS_MKDIR_P' does not accept options, but
`MKDIR_P' supports the `-m' option, e.g., a makefile might invoke
`$(MKDIR_P) -m 0 dir' to create an inaccessible directory, and
conversely a makefile should use `$(MKDIR_P) -- $(FOO)' if FOO
might yield a value that begins with `-'. Finally, `AS_MKDIR_P'
does not check for race condition vulnerability, whereas
`AC_PROG_MKDIR_P' does.
`@MKDIR_P@' is special, as its value may vary for different
configuration files.
The result of the test can be overridden by setting the variable
`MKDIR_P' or the cache variable `ac_cv_path_mkdir'.
-- Macro: AC_PROG_LEX
If `flex' is found, set output variable `LEX' to `flex' and
`LEXLIB' to `-lfl', if that library is in a standard place.
Otherwise set `LEX' to `lex' and `LEXLIB' to `-ll', if found. If
neither variant is available, set `LEX' to `:'; for packages that
ship the generated `file.yy.c' alongside the source `file.l', this
default allows users without a lexer generator to still build the
package even if the timestamp for `file.l' is inadvertently
changed.
Define `YYTEXT_POINTER' if `yytext' defaults to `char *' instead
of to `char []'. Also set output variable `LEX_OUTPUT_ROOT' to
the base of the file name that the lexer generates; usually
`lex.yy', but sometimes something else. These results vary
according to whether `lex' or `flex' is being used.
You are encouraged to use Flex in your sources, since it is both
more pleasant to use than plain Lex and the C source it produces
is portable. In order to ensure portability, however, you must
either provide a function `yywrap' or, if you don't use it (e.g.,
your scanner has no `#include'-like feature), simply include a
`%noyywrap' statement in the scanner's source. Once this done,
the scanner is portable (unless _you_ felt free to use nonportable
constructs) and does not depend on any library. In this case, and
in this case only, it is suggested that you use this Autoconf
snippet:
AC_PROG_LEX
if test "x$LEX" != xflex; then
LEX="$SHELL $missing_dir/missing flex"
AC_SUBST([LEX_OUTPUT_ROOT], [lex.yy])
AC_SUBST([LEXLIB], [''])
fi
The shell script `missing' can be found in the Automake
distribution.
Remember that the user may have supplied an alternate location in
`LEX', so if Flex is required, it is better to check that the user
provided something sufficient by parsing the output of `$LEX
--version' than by simply relying on `test "x$LEX" = xflex'.
To ensure backward compatibility, Automake's `AM_PROG_LEX' invokes
(indirectly) this macro twice, which causes an annoying but benign
"`AC_PROG_LEX' invoked multiple times" warning. Future versions
of Automake will fix this issue; meanwhile, just ignore this
message.
As part of running the test, this macro may delete any file in the
configuration directory named `lex.yy.c' or `lexyy.c'.
The result of this test can be influenced by setting the variable
`LEX' or the cache variable `ac_cv_prog_LEX'.
-- Macro: AC_PROG_LN_S
If `ln -s' works on the current file system (the operating system
and file system support symbolic links), set the output variable
`LN_S' to `ln -s'; otherwise, if `ln' works, set `LN_S' to `ln',
and otherwise set it to `cp -pR'.
If you make a link in a directory other than the current
directory, its meaning depends on whether `ln' or `ln -s' is used.
To safely create links using `$(LN_S)', either find out which form
is used and adjust the arguments, or always invoke `ln' in the
directory where the link is to be created.
In other words, it does not work to do:
$(LN_S) foo /x/bar
Instead, do:
(cd /x && $(LN_S) foo bar)
-- Macro: AC_PROG_RANLIB
Set output variable `RANLIB' to `ranlib' if `ranlib' is found, and
otherwise to `:' (do nothing).
-- Macro: AC_PROG_SED
Set output variable `SED' to a Sed implementation that conforms to
Posix and does not have arbitrary length limits. Report an error
if no acceptable Sed is found. *Note Limitations of Usual Tools:
sed, for more information about portability problems with Sed.
The result of this test can be overridden by setting the `SED'
variable and is cached in the `ac_cv_path_SED' variable.
-- Macro: AC_PROG_YACC
If `bison' is found, set output variable `YACC' to `bison -y'.
Otherwise, if `byacc' is found, set `YACC' to `byacc'. Otherwise
set `YACC' to `yacc'. The result of this test can be influenced
by setting the variable `YACC' or the cache variable
`ac_cv_prog_YACC'.
File: autoconf.info, Node: Generic Programs, Prev: Particular Programs, Up: Alternative Programs
5.2.2 Generic Program and File Checks
-------------------------------------
These macros are used to find programs not covered by the "particular"
test macros. If you need to check the behavior of a program as well as
find out whether it is present, you have to write your own test for it
(*note Writing Tests::). By default, these macros use the environment
variable `PATH'. If you need to check for a program that might not be
in the user's `PATH', you can pass a modified path to use instead, like
this:
AC_PATH_PROG([INETD], [inetd], [/usr/libexec/inetd],
[$PATH$PATH_SEPARATOR/usr/libexec$PATH_SEPARATOR]dnl
[/usr/sbin$PATH_SEPARATOR/usr/etc$PATH_SEPARATOR/etc])
You are strongly encouraged to declare the VARIABLE passed to
`AC_CHECK_PROG' etc. as precious. *Note Setting Output Variables::,
`AC_ARG_VAR', for more details.
-- Macro: AC_CHECK_PROG (VARIABLE, PROG-TO-CHECK-FOR, VALUE-IF-FOUND,
[VALUE-IF-NOT-FOUND], [PATH = `$PATH'], [REJECT])
Check whether program PROG-TO-CHECK-FOR exists in PATH. If it is
found, set VARIABLE to VALUE-IF-FOUND, otherwise to
VALUE-IF-NOT-FOUND, if given. Always pass over REJECT (an
absolute file name) even if it is the first found in the search
path; in that case, set VARIABLE using the absolute file name of
the PROG-TO-CHECK-FOR found that is not REJECT. If VARIABLE was
already set, do nothing. Calls `AC_SUBST' for VARIABLE. The
result of this test can be overridden by setting the VARIABLE
variable or the cache variable `ac_cv_prog_VARIABLE'.
-- Macro: AC_CHECK_PROGS (VARIABLE, PROGS-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH = `$PATH'])
Check for each program in the blank-separated list
PROGS-TO-CHECK-FOR existing in the PATH. If one is found, set
VARIABLE to the name of that program. Otherwise, continue
checking the next program in the list. If none of the programs in
the list are found, set VARIABLE to VALUE-IF-NOT-FOUND; if
VALUE-IF-NOT-FOUND is not specified, the value of VARIABLE is not
changed. Calls `AC_SUBST' for VARIABLE. The result of this test
can be overridden by setting the VARIABLE variable or the cache
variable `ac_cv_prog_VARIABLE'.
-- Macro: AC_CHECK_TARGET_TOOL (VARIABLE, PROG-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH = `$PATH'])
Like `AC_CHECK_PROG', but first looks for PROG-TO-CHECK-FOR with a
prefix of the target type as determined by `AC_CANONICAL_TARGET',
followed by a dash (*note Canonicalizing::). If the tool cannot
be found with a prefix, and if the build and target types are
equal, then it is also searched for without a prefix.
As noted in *note Specifying Target Triplets::, the target is
rarely specified, because most of the time it is the same as the
host: it is the type of system for which any compiler tool in the
package produces code. What this macro looks for is, for example,
_a tool (assembler, linker, etc.) that the compiler driver (`gcc'
for the GNU C Compiler) uses to produce objects, archives or
executables_.
-- Macro: AC_CHECK_TOOL (VARIABLE, PROG-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH = `$PATH'])
Like `AC_CHECK_PROG', but first looks for PROG-TO-CHECK-FOR with a
prefix of the host type as specified by `--host', followed by a
dash. For example, if the user runs `configure --build=x86_64-gnu
--host=i386-gnu', then this call:
AC_CHECK_TOOL([RANLIB], [ranlib], [:])
sets `RANLIB' to `i386-gnu-ranlib' if that program exists in PATH,
or otherwise to `ranlib' if that program exists in PATH, or to `:'
if neither program exists.
When cross-compiling, this macro will issue a warning if no program
prefixed with the host type could be found. For more information,
see *note Specifying Target Triplets::.
-- Macro: AC_CHECK_TARGET_TOOLS (VARIABLE, PROGS-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH = `$PATH'])
Like `AC_CHECK_TARGET_TOOL', each of the tools in the list
PROGS-TO-CHECK-FOR are checked with a prefix of the target type as
determined by `AC_CANONICAL_TARGET', followed by a dash (*note
Canonicalizing::). If none of the tools can be found with a
prefix, and if the build and target types are equal, then the
first one without a prefix is used. If a tool is found, set
VARIABLE to the name of that program. If none of the tools in the
list are found, set VARIABLE to VALUE-IF-NOT-FOUND; if
VALUE-IF-NOT-FOUND is not specified, the value of VARIABLE is not
changed. Calls `AC_SUBST' for VARIABLE.
-- Macro: AC_CHECK_TOOLS (VARIABLE, PROGS-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH = `$PATH'])
Like `AC_CHECK_TOOL', each of the tools in the list
PROGS-TO-CHECK-FOR are checked with a prefix of the host type as
determined by `AC_CANONICAL_HOST', followed by a dash (*note
Canonicalizing::). If none of the tools can be found with a
prefix, then the first one without a prefix is used. If a tool is
found, set VARIABLE to the name of that program. If none of the
tools in the list are found, set VARIABLE to VALUE-IF-NOT-FOUND; if
VALUE-IF-NOT-FOUND is not specified, the value of VARIABLE is not
changed. Calls `AC_SUBST' for VARIABLE.
When cross-compiling, this macro will issue a warning if no program
prefixed with the host type could be found. For more information,
see *note Specifying Target Triplets::.
-- Macro: AC_PATH_PROG (VARIABLE, PROG-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH = `$PATH'])
Like `AC_CHECK_PROG', but set VARIABLE to the absolute name of
PROG-TO-CHECK-FOR if found. The result of this test can be
overridden by setting the VARIABLE variable. A positive result of
this test is cached in the `ac_cv_path_VARIABLE' variable.
-- Macro: AC_PATH_PROGS (VARIABLE, PROGS-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH = `$PATH'])
Like `AC_CHECK_PROGS', but if any of PROGS-TO-CHECK-FOR are found,
set VARIABLE to the absolute name of the program found. The
result of this test can be overridden by setting the VARIABLE
variable. A positive result of this test is cached in the
`ac_cv_path_VARIABLE' variable.
-- Macro: AC_PATH_PROGS_FEATURE_CHECK (VARIABLE, PROGS-TO-CHECK-FOR,
FEATURE-TEST, [ACTION-IF-NOT-FOUND], [PATH = `$PATH'])
This macro was introduced in Autoconf 2.62. If VARIABLE is not
empty, then set the cache variable `ac_cv_path_VARIABLE' to its
value. Otherwise, check for each program in the blank-separated
list PROGS-TO-CHECK-FOR existing in PATH. For each program found,
execute FEATURE-TEST with `ac_path_VARIABLE' set to the absolute
name of the candidate program. If no invocation of FEATURE-TEST
sets the shell variable `ac_cv_path_VARIABLE', then
ACTION-IF-NOT-FOUND is executed. FEATURE-TEST will be run even
when `ac_cv_path_VARIABLE' is set, to provide the ability to
choose a better candidate found later in PATH; to accept the
current setting and bypass all further checks, FEATURE-TEST can
execute `ac_path_VARIABLE_found=:'.
Note that this macro has some subtle differences from
`AC_CHECK_PROGS'. It is designed to be run inside `AC_CACHE_VAL',
therefore, it should have no side effects. In particular,
VARIABLE is not set to the final value of `ac_cv_path_VARIABLE',
nor is `AC_SUBST' automatically run. Also, on failure, any action
can be performed, whereas `AC_CHECK_PROGS' only performs
`VARIABLE=VALUE-IF-NOT-FOUND'.
Here is an example, similar to what Autoconf uses in its own
configure script. It will search for an implementation of `m4'
that supports the `indir' builtin, even if it goes by the name
`gm4' or is not the first implementation on `PATH'.
AC_CACHE_CHECK([for m4 that supports indir], [ac_cv_path_M4],
[AC_PATH_PROGS_FEATURE_CHECK([M4], [m4 gm4],
[[m4out=`echo 'changequote([,])indir([divnum])' | $ac_path_M4`
test "x$m4out" = x0 \
&& ac_cv_path_M4=$ac_path_M4 ac_path_M4_found=:]],
[AC_MSG_ERROR([could not find m4 that supports indir])])])
AC_SUBST([M4], [$ac_cv_path_M4])
-- Macro: AC_PATH_TARGET_TOOL (VARIABLE, PROG-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH = `$PATH'])
Like `AC_CHECK_TARGET_TOOL', but set VARIABLE to the absolute name
of the program if it is found.
-- Macro: AC_PATH_TOOL (VARIABLE, PROG-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH = `$PATH'])
Like `AC_CHECK_TOOL', but set VARIABLE to the absolute name of the
program if it is found.
When cross-compiling, this macro will issue a warning if no program
prefixed with the host type could be found. For more information,
see *note Specifying Target Triplets::.
File: autoconf.info, Node: Files, Next: Libraries, Prev: Alternative Programs, Up: Existing Tests
5.3 Files
=========
You might also need to check for the existence of files. Before using
these macros, ask yourself whether a runtime test might not be a better
solution. Be aware that, like most Autoconf macros, they test a feature
of the host machine, and therefore, they die when cross-compiling.
-- Macro: AC_CHECK_FILE (FILE, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
Check whether file FILE exists on the native system. If it is
found, execute ACTION-IF-FOUND, otherwise do ACTION-IF-NOT-FOUND,
if given. The result of this test is cached in the
`ac_cv_file_FILE' variable, with characters not suitable for a
variable name mapped to underscores.
-- Macro: AC_CHECK_FILES (FILES, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
Executes `AC_CHECK_FILE' once for each file listed in FILES.
Additionally, defines `HAVE_FILE' (*note Standard Symbols::) for
each file found. The results of each test are cached in the
`ac_cv_file_FILE' variable, with characters not suitable for a
variable name mapped to underscores.
File: autoconf.info, Node: Libraries, Next: Library Functions, Prev: Files, Up: Existing Tests
5.4 Library Files
=================
The following macros check for the presence of certain C, C++, Fortran,
or Go library archive files.
-- Macro: AC_CHECK_LIB (LIBRARY, FUNCTION, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [OTHER-LIBRARIES])
Test whether the library LIBRARY is available by trying to link a
test program that calls function FUNCTION with the library.
FUNCTION should be a function provided by the library. Use the
base name of the library; e.g., to check for `-lmp', use `mp' as
the LIBRARY argument.
ACTION-IF-FOUND is a list of shell commands to run if the link
with the library succeeds; ACTION-IF-NOT-FOUND is a list of shell
commands to run if the link fails. If ACTION-IF-FOUND is not
specified, the default action prepends `-lLIBRARY' to `LIBS' and
defines `HAVE_LIBLIBRARY' (in all capitals). This macro is
intended to support building `LIBS' in a right-to-left
(least-dependent to most-dependent) fashion such that library
dependencies are satisfied as a natural side effect of consecutive
tests. Linkers are sensitive to library ordering so the order in
which `LIBS' is generated is important to reliable detection of
libraries.
If linking with LIBRARY results in unresolved symbols that would
be resolved by linking with additional libraries, give those
libraries as the OTHER-LIBRARIES argument, separated by spaces:
e.g., `-lXt -lX11'. Otherwise, this macro may fail to detect that
LIBRARY is present, because linking the test program can fail with
unresolved symbols. The OTHER-LIBRARIES argument should be
limited to cases where it is desirable to test for one library in
the presence of another that is not already in `LIBS'.
`AC_CHECK_LIB' requires some care in usage, and should be avoided
in some common cases. Many standard functions like `gethostbyname'
appear in the standard C library on some hosts, and in special
libraries like `nsl' on other hosts. On some hosts the special
libraries contain variant implementations that you may not want to
use. These days it is normally better to use
`AC_SEARCH_LIBS([gethostbyname], [nsl])' instead of
`AC_CHECK_LIB([nsl], [gethostbyname])'.
The result of this test is cached in the
`ac_cv_lib_LIBRARY_FUNCTION' variable.
-- Macro: AC_SEARCH_LIBS (FUNCTION, SEARCH-LIBS, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [OTHER-LIBRARIES])
Search for a library defining FUNCTION if it's not already
available. This equates to calling
`AC_LINK_IFELSE([AC_LANG_CALL([], [FUNCTION])])' first with no
libraries, then for each library listed in SEARCH-LIBS.
Prepend `-lLIBRARY' to `LIBS' for the first library found to
contain FUNCTION, and run ACTION-IF-FOUND. If the function is not
found, run ACTION-IF-NOT-FOUND.
If linking with LIBRARY results in unresolved symbols that would
be resolved by linking with additional libraries, give those
libraries as the OTHER-LIBRARIES argument, separated by spaces:
e.g., `-lXt -lX11'. Otherwise, this macro fails to detect that
FUNCTION is present, because linking the test program always fails
with unresolved symbols.
The result of this test is cached in the `ac_cv_search_FUNCTION'
variable as `none required' if FUNCTION is already available, as
`no' if no library containing FUNCTION was found, otherwise as the
`-lLIBRARY' option that needs to be prepended to `LIBS'.
File: autoconf.info, Node: Library Functions, Next: Header Files, Prev: Libraries, Up: Existing Tests
5.5 Library Functions
=====================
The following macros check for particular C library functions. If
there is no macro specifically defined to check for a function you need,
and you don't need to check for any special properties of it, then you
can use one of the general function-check macros.
* Menu:
* Function Portability:: Pitfalls with usual functions
* Particular Functions:: Special handling to find certain functions
* Generic Functions:: How to find other functions
File: autoconf.info, Node: Function Portability, Next: Particular Functions, Up: Library Functions
5.5.1 Portability of C Functions
--------------------------------
Most usual functions can either be missing, or be buggy, or be limited
on some architectures. This section tries to make an inventory of these
portability issues. By definition, this list always requires
additions. A much more complete list is maintained by the Gnulib
project (*note Gnulib::), covering *note Current Posix Functions:
(gnulib)Function Substitutes, *note Legacy Functions: (gnulib)Legacy
Function Substitutes, and *note Glibc Functions: (gnulib)Glibc Function
Substitutes. Please help us keep the gnulib list as complete as
possible.
`exit'
On ancient hosts, `exit' returned `int'. This is because `exit'
predates `void', and there was a long tradition of it returning
`int'.
On current hosts, the problem more likely is that `exit' is not
declared, due to C++ problems of some sort or another. For this
reason we suggest that test programs not invoke `exit', but return
from `main' instead.
`free'
The C standard says a call `free (NULL)' does nothing, but some
old systems don't support this (e.g., NextStep).
`isinf'
`isnan'
The C99 standard says that `isinf' and `isnan' are macros. On
some systems just macros are available (e.g., HP-UX and Solaris
10), on some systems both macros and functions (e.g., glibc
2.3.2), and on some systems only functions (e.g., IRIX 6 and
Solaris 9). In some cases these functions are declared in
nonstandard headers like `' and defined in non-default
libraries like `-lm' or `-lsunmath'.
The C99 `isinf' and `isnan' macros work correctly with `long
double' arguments, but pre-C99 systems that use functions
typically assume `double' arguments. On such a system, `isinf'
incorrectly returns true for a finite `long double' argument that
is outside the range of `double'.
The best workaround for these issues is to use gnulib modules
`isinf' and `isnan' (*note Gnulib::). But a lighter weight
solution involves code like the following.
#include
#ifndef isnan
# define isnan(x) \
(sizeof (x) == sizeof (long double) ? isnan_ld (x) \
: sizeof (x) == sizeof (double) ? isnan_d (x) \
: isnan_f (x))
static inline int isnan_f (float x) { return x != x; }
static inline int isnan_d (double x) { return x != x; }
static inline int isnan_ld (long double x) { return x != x; }
#endif
#ifndef isinf
# define isinf(x) \
(sizeof (x) == sizeof (long double) ? isinf_ld (x) \
: sizeof (x) == sizeof (double) ? isinf_d (x) \
: isinf_f (x))
static inline int isinf_f (float x)
{ return !isnan (x) && isnan (x - x); }
static inline int isinf_d (double x)
{ return !isnan (x) && isnan (x - x); }
static inline int isinf_ld (long double x)
{ return !isnan (x) && isnan (x - x); }
#endif
Use `AC_C_INLINE' (*note C Compiler::) so that this code works on
compilers that lack the `inline' keyword. Some optimizing
compilers mishandle these definitions, but systems with that bug
typically have many other floating point corner-case compliance
problems anyway, so it's probably not worth worrying about.
`malloc'
The C standard says a call `malloc (0)' is implementation
dependent. It can return either `NULL' or a new non-null pointer.
The latter is more common (e.g., the GNU C Library) but is by no
means universal. `AC_FUNC_MALLOC' can be used to insist on
non-`NULL' (*note Particular Functions::).
`putenv'
Posix prefers `setenv' to `putenv'; among other things, `putenv'
is not required of all Posix implementations, but `setenv' is.
Posix specifies that `putenv' puts the given string directly in
`environ', but some systems make a copy of it instead (e.g., glibc
2.0, or BSD). And when a copy is made, `unsetenv' might not free
it, causing a memory leak (e.g., FreeBSD 4).
On some systems `putenv ("FOO")' removes `FOO' from the
environment, but this is not standard usage and it dumps core on
some systems (e.g., AIX).
On MinGW, a call `putenv ("FOO=")' removes `FOO' from the
environment, rather than inserting it with an empty value.
`realloc'
The C standard says a call `realloc (NULL, size)' is equivalent to
`malloc (size)', but some old systems don't support this (e.g.,
NextStep).
`signal' handler
Normally `signal' takes a handler function with a return type of
`void', but some old systems required `int' instead. Any actual
`int' value returned is not used; this is only a difference in the
function prototype demanded.
All systems we know of in current use return `void'. The `int'
was to support K&R C, where of course `void' is not available.
The obsolete macro `AC_TYPE_SIGNAL' (*note AC_TYPE_SIGNAL::) can
be used to establish the correct type in all cases.
In most cases, it is more robust to use `sigaction' when it is
available, rather than `signal'.
`snprintf'
The C99 standard says that if the output array isn't big enough
and if no other errors occur, `snprintf' and `vsnprintf' truncate
the output and return the number of bytes that ought to have been
produced. Some older systems return the truncated length (e.g.,
GNU C Library 2.0.x or IRIX 6.5), some a negative value (e.g.,
earlier GNU C Library versions), and some the buffer length
without truncation (e.g., 32-bit Solaris 7). Also, some buggy
older systems ignore the length and overrun the buffer (e.g.,
64-bit Solaris 7).
`sprintf'
The C standard says `sprintf' and `vsprintf' return the number of
bytes written. On some ancient systems (SunOS 4 for instance)
they return the buffer pointer instead, but these no longer need
to be worried about.
`sscanf'
On various old systems, e.g., HP-UX 9, `sscanf' requires that its
input string be writable (though it doesn't actually change it).
This can be a problem when using `gcc' since it normally puts
constant strings in read-only memory (*note Incompatibilities of
GCC: (gcc)Incompatibilities.). Apparently in some cases even
having format strings read-only can be a problem.
`strerror_r'
Posix specifies that `strerror_r' returns an `int', but many
systems (e.g., GNU C Library version 2.2.4) provide a different
version returning a `char *'. `AC_FUNC_STRERROR_R' can detect
which is in use (*note Particular Functions::).
`strnlen'
AIX 4.3 provides a broken version which produces the following
results:
strnlen ("foobar", 0) = 0
strnlen ("foobar", 1) = 3
strnlen ("foobar", 2) = 2
strnlen ("foobar", 3) = 1
strnlen ("foobar", 4) = 0
strnlen ("foobar", 5) = 6
strnlen ("foobar", 6) = 6
strnlen ("foobar", 7) = 6
strnlen ("foobar", 8) = 6
strnlen ("foobar", 9) = 6
`sysconf'
`_SC_PAGESIZE' is standard, but some older systems (e.g., HP-UX 9)
have `_SC_PAGE_SIZE' instead. This can be tested with `#ifdef'.
`unlink'
The Posix spec says that `unlink' causes the given file to be
removed only after there are no more open file handles for it.
Some non-Posix hosts have trouble with this requirement, though,
and some DOS variants even corrupt the file system.
`unsetenv'
On MinGW, `unsetenv' is not available, but a variable `FOO' can be
removed with a call `putenv ("FOO=")', as described under `putenv'
above.
`va_copy'
The C99 standard provides `va_copy' for copying `va_list'
variables. It may be available in older environments too, though
possibly as `__va_copy' (e.g., `gcc' in strict pre-C99 mode).
These can be tested with `#ifdef'. A fallback to `memcpy (&dst,
&src, sizeof (va_list))' gives maximum portability.
`va_list'
`va_list' is not necessarily just a pointer. It can be a `struct'
(e.g., `gcc' on Alpha), which means `NULL' is not portable. Or it
can be an array (e.g., `gcc' in some PowerPC configurations),
which means as a function parameter it can be effectively
call-by-reference and library routines might modify the value back
in the caller (e.g., `vsnprintf' in the GNU C Library 2.1).
Signed `>>'
Normally the C `>>' right shift of a signed type replicates the
high bit, giving a so-called "arithmetic" shift. But care should
be taken since Standard C doesn't require that behavior. On those
few processors without a native arithmetic shift (for instance Cray
vector systems) zero bits may be shifted in, the same as a shift
of an unsigned type.
Integer `/'
C divides signed integers by truncating their quotient toward zero,
yielding the same result as Fortran. However, before C99 the
standard allowed C implementations to take the floor or ceiling of
the quotient in some cases. Hardly any implementations took
advantage of this freedom, though, and it's probably not worth
worrying about this issue nowadays.
File: autoconf.info, Node: Particular Functions, Next: Generic Functions, Prev: Function Portability, Up: Library Functions
5.5.2 Particular Function Checks
--------------------------------
These macros check for particular C functions--whether they exist, and
in some cases how they respond when given certain arguments.
-- Macro: AC_FUNC_ALLOCA
Check how to get `alloca'. Tries to get a builtin version by
checking for `alloca.h' or the predefined C preprocessor macros
`__GNUC__' and `_AIX'. If this macro finds `alloca.h', it defines
`HAVE_ALLOCA_H'.
If those attempts fail, it looks for the function in the standard C
library. If any of those methods succeed, it defines
`HAVE_ALLOCA'. Otherwise, it sets the output variable `ALLOCA' to
`${LIBOBJDIR}alloca.o' and defines `C_ALLOCA' (so programs can
periodically call `alloca (0)' to garbage collect). This variable
is separate from `LIBOBJS' so multiple programs can share the
value of `ALLOCA' without needing to create an actual library, in
case only some of them use the code in `LIBOBJS'. The
`${LIBOBJDIR}' prefix serves the same purpose as in `LIBOBJS'
(*note AC_LIBOBJ vs LIBOBJS::).
This macro does not try to get `alloca' from the System V R3
`libPW' or the System V R4 `libucb' because those libraries
contain some incompatible functions that cause trouble. Some
versions do not even contain `alloca' or contain a buggy version.
If you still want to use their `alloca', use `ar' to extract
`alloca.o' from them instead of compiling `alloca.c'.
Source files that use `alloca' should start with a piece of code
like the following, to declare it properly.
#ifdef STDC_HEADERS
# include
# include
#else
# ifdef HAVE_STDLIB_H
# include
# endif
#endif
#ifdef HAVE_ALLOCA_H
# include
#elif !defined alloca
# ifdef __GNUC__
# define alloca __builtin_alloca
# elif defined _AIX
# define alloca __alloca
# elif defined _MSC_VER
# include
# define alloca _alloca
# elif !defined HAVE_ALLOCA
# ifdef __cplusplus
extern "C"
# endif
void *alloca (size_t);
# endif
#endif
-- Macro: AC_FUNC_CHOWN
If the `chown' function is available and works (in particular, it
should accept `-1' for `uid' and `gid'), define `HAVE_CHOWN'. The
result of this macro is cached in the `ac_cv_func_chown_works'
variable.
-- Macro: AC_FUNC_CLOSEDIR_VOID
If the `closedir' function does not return a meaningful value,
define `CLOSEDIR_VOID'. Otherwise, callers ought to check its
return value for an error indicator.
Currently this test is implemented by running a test program. When
cross compiling the pessimistic assumption that `closedir' does not
return a meaningful value is made.
The result of this macro is cached in the
`ac_cv_func_closedir_void' variable.
This macro is obsolescent, as `closedir' returns a meaningful value
on current systems. New programs need not use this macro.
-- Macro: AC_FUNC_ERROR_AT_LINE
If the `error_at_line' function is not found, require an
`AC_LIBOBJ' replacement of `error'.
The result of this macro is cached in the `ac_cv_lib_error_at_line'
variable.
The `AC_FUNC_ERROR_AT_LINE' macro is obsolescent. New programs
should use Gnulib's `error' module. *Note Gnulib::.
-- Macro: AC_FUNC_FNMATCH
If the `fnmatch' function conforms to Posix, define
`HAVE_FNMATCH'. Detect common implementation bugs, for example,
the bugs in Solaris 2.4.
Unlike the other specific `AC_FUNC' macros, `AC_FUNC_FNMATCH' does
not replace a broken/missing `fnmatch'. This is for historical
reasons. See `AC_REPLACE_FNMATCH' below.
The result of this macro is cached in the
`ac_cv_func_fnmatch_works' variable.
This macro is obsolescent. New programs should use Gnulib's
`fnmatch-posix' module. *Note Gnulib::.
-- Macro: AC_FUNC_FNMATCH_GNU
Behave like `AC_REPLACE_FNMATCH' (_replace_) but also test whether
`fnmatch' supports GNU extensions. Detect common implementation
bugs, for example, the bugs in the GNU C Library 2.1.
The result of this macro is cached in the `ac_cv_func_fnmatch_gnu'
variable.
This macro is obsolescent. New programs should use Gnulib's
`fnmatch-gnu' module. *Note Gnulib::.
-- Macro: AC_FUNC_FORK
This macro checks for the `fork' and `vfork' functions. If a
working `fork' is found, define `HAVE_WORKING_FORK'. This macro
checks whether `fork' is just a stub by trying to run it.
If `vfork.h' is found, define `HAVE_VFORK_H'. If a working
`vfork' is found, define `HAVE_WORKING_VFORK'. Otherwise, define
`vfork' to be `fork' for backward compatibility with previous
versions of `autoconf'. This macro checks for several known
errors in implementations of `vfork' and considers the system to
not have a working `vfork' if it detects any of them. It is not
considered to be an implementation error if a child's invocation
of `signal' modifies the parent's signal handler, since child
processes rarely change their signal handlers.
Since this macro defines `vfork' only for backward compatibility
with previous versions of `autoconf' you're encouraged to define it
yourself in new code:
#ifndef HAVE_WORKING_VFORK
# define vfork fork
#endif
The results of this macro are cached in the `ac_cv_func_fork_works'
and `ac_cv_func_vfork_works' variables. In order to override the
test, you also need to set the `ac_cv_func_fork' and
`ac_cv_func_vfork' variables.
-- Macro: AC_FUNC_FSEEKO
If the `fseeko' function is available, define `HAVE_FSEEKO'.
Define `_LARGEFILE_SOURCE' if necessary to make the prototype
visible on some systems (e.g., glibc 2.2). Otherwise linkage
problems may occur when compiling with `AC_SYS_LARGEFILE' on
largefile-sensitive systems where `off_t' does not default to a
64bit entity. All systems with `fseeko' also supply `ftello'.
-- Macro: AC_FUNC_GETGROUPS
If the `getgroups' function is available and works (unlike on
Ultrix 4.3, where `getgroups (0, 0)' always fails), define
`HAVE_GETGROUPS'. Set `GETGROUPS_LIBS' to any libraries needed to
get that function. This macro runs `AC_TYPE_GETGROUPS'.
-- Macro: AC_FUNC_GETLOADAVG
Check how to get the system load averages. To perform its tests
properly, this macro needs the file `getloadavg.c'; therefore, be
sure to set the `AC_LIBOBJ' replacement directory properly (see
*note Generic Functions::, `AC_CONFIG_LIBOBJ_DIR').
If the system has the `getloadavg' function, define
`HAVE_GETLOADAVG', and set `GETLOADAVG_LIBS' to any libraries
necessary to get that function. Also add `GETLOADAVG_LIBS' to
`LIBS'. Otherwise, require an `AC_LIBOBJ' replacement for
`getloadavg' with source code in `DIR/getloadavg.c', and possibly
define several other C preprocessor macros and output variables:
1. Define `C_GETLOADAVG'.
2. Define `SVR4', `DGUX', `UMAX', or `UMAX4_3' if on those
systems.
3. If `nlist.h' is found, define `HAVE_NLIST_H'.
4. If `struct nlist' has an `n_un.n_name' member, define
`HAVE_STRUCT_NLIST_N_UN_N_NAME'. The obsolete symbol
`NLIST_NAME_UNION' is still defined, but do not depend upon
it.
5. Programs may need to be installed set-group-ID (or
set-user-ID) for `getloadavg' to work. In this case, define
`GETLOADAVG_PRIVILEGED', set the output variable `NEED_SETGID'
to `true' (and otherwise to `false'), and set `KMEM_GROUP' to
the name of the group that should own the installed program.
The `AC_FUNC_GETLOADAVG' macro is obsolescent. New programs should
use Gnulib's `getloadavg' module. *Note Gnulib::.
-- Macro: AC_FUNC_GETMNTENT
Check for `getmntent' in the standard C library, and then in the
`sun', `seq', and `gen' libraries, for UNICOS, IRIX 4, PTX, and
UnixWare, respectively. Then, if `getmntent' is available, define
`HAVE_GETMNTENT' and set `ac_cv_func_getmntent' to `yes'.
Otherwise set `ac_cv_func_getmntent' to `no'.
The result of this macro can be overridden by setting the cache
variable `ac_cv_search_getmntent'.
-- Macro: AC_FUNC_GETPGRP
Define `GETPGRP_VOID' if it is an error to pass 0 to `getpgrp';
this is the Posix behavior. On older BSD systems, you must pass 0
to `getpgrp', as it takes an argument and behaves like Posix's
`getpgid'.
#ifdef GETPGRP_VOID
pid = getpgrp ();
#else
pid = getpgrp (0);
#endif
This macro does not check whether `getpgrp' exists at all; if you
need to work in that situation, first call `AC_CHECK_FUNC' for
`getpgrp'.
The result of this macro is cached in the `ac_cv_func_getpgrp_void'
variable.
This macro is obsolescent, as current systems have a `getpgrp'
whose signature conforms to Posix. New programs need not use this
macro.
-- Macro: AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK
If `link' is a symbolic link, then `lstat' should treat `link/'
the same as `link/.'. However, many older `lstat' implementations
incorrectly ignore trailing slashes.
It is safe to assume that if `lstat' incorrectly ignores trailing
slashes, then other symbolic-link-aware functions like `unlink'
also incorrectly ignore trailing slashes.
If `lstat' behaves properly, define
`LSTAT_FOLLOWS_SLASHED_SYMLINK', otherwise require an `AC_LIBOBJ'
replacement of `lstat'.
The result of this macro is cached in the
`ac_cv_func_lstat_dereferences_slashed_symlink' variable.
The `AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK' macro is obsolescent.
New programs should use Gnulib's `lstat' module. *Note Gnulib::.
-- Macro: AC_FUNC_MALLOC
If the `malloc' function is compatible with the GNU C library
`malloc' (i.e., `malloc (0)' returns a valid pointer), define
`HAVE_MALLOC' to 1. Otherwise define `HAVE_MALLOC' to 0, ask for
an `AC_LIBOBJ' replacement for `malloc', and define `malloc' to
`rpl_malloc' so that the native `malloc' is not used in the main
project.
Typically, the replacement file `malloc.c' should look like (note
the `#undef malloc'):
#include
#undef malloc
#include
void *malloc ();
/* Allocate an N-byte block of memory from the heap.
If N is zero, allocate a 1-byte block. */
void *
rpl_malloc (size_t n)
{
if (n == 0)
n = 1;
return malloc (n);
}
The result of this macro is cached in the
`ac_cv_func_malloc_0_nonnull' variable.
-- Macro: AC_FUNC_MBRTOWC
Define `HAVE_MBRTOWC' to 1 if the function `mbrtowc' and the type
`mbstate_t' are properly declared.
The result of this macro is cached in the `ac_cv_func_mbrtowc'
variable.
-- Macro: AC_FUNC_MEMCMP
If the `memcmp' function is not available, or does not work on
8-bit data (like the one on SunOS 4.1.3), or fails when comparing
16 bytes or more and with at least one buffer not starting on a
4-byte boundary (such as the one on NeXT x86 OpenStep), require an
`AC_LIBOBJ' replacement for `memcmp'.
The result of this macro is cached in the
`ac_cv_func_memcmp_working' variable.
This macro is obsolescent, as current systems have a working
`memcmp'. New programs need not use this macro.
-- Macro: AC_FUNC_MKTIME
If the `mktime' function is not available, or does not work
correctly, require an `AC_LIBOBJ' replacement for `mktime'. For
the purposes of this test, `mktime' should conform to the Posix
standard and should be the inverse of `localtime'.
The result of this macro is cached in the
`ac_cv_func_working_mktime' variable.
The `AC_FUNC_MKTIME' macro is obsolescent. New programs should
use Gnulib's `mktime' module. *Note Gnulib::.
-- Macro: AC_FUNC_MMAP
If the `mmap' function exists and works correctly, define
`HAVE_MMAP'. This checks only private fixed mapping of
already-mapped memory.
The result of this macro is cached in the
`ac_cv_func_mmap_fixed_mapped' variable.
-- Macro: AC_FUNC_OBSTACK
If the obstacks are found, define `HAVE_OBSTACK', else require an
`AC_LIBOBJ' replacement for `obstack'.
The result of this macro is cached in the `ac_cv_func_obstack'
variable.
-- Macro: AC_FUNC_REALLOC
If the `realloc' function is compatible with the GNU C library
`realloc' (i.e., `realloc (NULL, 0)' returns a valid pointer),
define `HAVE_REALLOC' to 1. Otherwise define `HAVE_REALLOC' to 0,
ask for an `AC_LIBOBJ' replacement for `realloc', and define
`realloc' to `rpl_realloc' so that the native `realloc' is not
used in the main project. See `AC_FUNC_MALLOC' for details.
The result of this macro is cached in the
`ac_cv_func_realloc_0_nonnull' variable.
-- Macro: AC_FUNC_SELECT_ARGTYPES
Determines the correct type to be passed for each of the `select'
function's arguments, and defines those types in
`SELECT_TYPE_ARG1', `SELECT_TYPE_ARG234', and `SELECT_TYPE_ARG5'
respectively. `SELECT_TYPE_ARG1' defaults to `int',
`SELECT_TYPE_ARG234' defaults to `int *', and `SELECT_TYPE_ARG5'
defaults to `struct timeval *'.
This macro is obsolescent, as current systems have a `select' whose
signature conforms to Posix. New programs need not use this macro.
-- Macro: AC_FUNC_SETPGRP
If `setpgrp' takes no argument (the Posix version), define
`SETPGRP_VOID'. Otherwise, it is the BSD version, which takes two
process IDs as arguments. This macro does not check whether
`setpgrp' exists at all; if you need to work in that situation,
first call `AC_CHECK_FUNC' for `setpgrp'.
The result of this macro is cached in the `ac_cv_func_setpgrp_void'
variable.
This macro is obsolescent, as current systems have a `setpgrp'
whose signature conforms to Posix. New programs need not use this
macro.
-- Macro: AC_FUNC_STAT
-- Macro: AC_FUNC_LSTAT
Determine whether `stat' or `lstat' have the bug that it succeeds
when given the zero-length file name as argument. The `stat' and
`lstat' from SunOS 4.1.4 and the Hurd (as of 1998-11-01) do this.
If it does, then define `HAVE_STAT_EMPTY_STRING_BUG' (or
`HAVE_LSTAT_EMPTY_STRING_BUG') and ask for an `AC_LIBOBJ'
replacement of it.
The results of these macros are cached in the
`ac_cv_func_stat_empty_string_bug' and the
`ac_cv_func_lstat_empty_string_bug' variables, respectively.
These macros are obsolescent, as no current systems have the bug.
New programs need not use these macros.
-- Macro: AC_FUNC_STRCOLL
If the `strcoll' function exists and works correctly, define
`HAVE_STRCOLL'. This does a bit more than
`AC_CHECK_FUNCS(strcoll)', because some systems have incorrect
definitions of `strcoll' that should not be used.
The result of this macro is cached in the
`ac_cv_func_strcoll_works' variable.
-- Macro: AC_FUNC_STRERROR_R
If `strerror_r' is available, define `HAVE_STRERROR_R', and if it
is declared, define `HAVE_DECL_STRERROR_R'. If it returns a `char
*' message, define `STRERROR_R_CHAR_P'; otherwise it returns an
`int' error number. The Thread-Safe Functions option of Posix
requires `strerror_r' to return `int', but many systems
(including, for example, version 2.2.4 of the GNU C Library)
return a `char *' value that is not necessarily equal to the
buffer argument.
The result of this macro is cached in the
`ac_cv_func_strerror_r_char_p' variable.
-- Macro: AC_FUNC_STRFTIME
Check for `strftime' in the `intl' library, for SCO Unix. Then,
if `strftime' is available, define `HAVE_STRFTIME'.
This macro is obsolescent, as no current systems require the `intl'
library for `strftime'. New programs need not use this macro.
-- Macro: AC_FUNC_STRTOD
If the `strtod' function does not exist or doesn't work correctly,
ask for an `AC_LIBOBJ' replacement of `strtod'. In this case,
because `strtod.c' is likely to need `pow', set the output
variable `POW_LIB' to the extra library needed.
This macro caches its result in the `ac_cv_func_strtod' variable
and depends upon the result in the `ac_cv_func_pow' variable.
The `AC_FUNC_STRTOD' macro is obsolescent. New programs should
use Gnulib's `strtod' module. *Note Gnulib::.
-- Macro: AC_FUNC_STRTOLD
If the `strtold' function exists and conforms to C99, define
`HAVE_STRTOLD'.
This macro caches its result in the `ac_cv_func_strtold' variable.
-- Macro: AC_FUNC_STRNLEN
If the `strnlen' function is not available, or is buggy (like the
one from AIX 4.3), require an `AC_LIBOBJ' replacement for it.
This macro caches its result in the `ac_cv_func_strnlen_working'
variable.
-- Macro: AC_FUNC_UTIME_NULL
If `utime (FILE, NULL)' sets FILE's timestamp to the present,
define `HAVE_UTIME_NULL'.
This macro caches its result in the `ac_cv_func_utime_null'
variable.
This macro is obsolescent, as all current systems have a `utime'
that behaves this way. New programs need not use this macro.
-- Macro: AC_FUNC_VPRINTF
If `vprintf' is found, define `HAVE_VPRINTF'. Otherwise, if
`_doprnt' is found, define `HAVE_DOPRNT'. (If `vprintf' is
available, you may assume that `vfprintf' and `vsprintf' are also
available.)
This macro is obsolescent, as all current systems have `vprintf'.
New programs need not use this macro.
-- Macro: AC_REPLACE_FNMATCH
If the `fnmatch' function does not conform to Posix (see
`AC_FUNC_FNMATCH'), ask for its `AC_LIBOBJ' replacement.
The files `fnmatch.c', `fnmatch_loop.c', and `fnmatch_.h' in the
`AC_LIBOBJ' replacement directory are assumed to contain a copy of
the source code of GNU `fnmatch'. If necessary, this source code
is compiled as an `AC_LIBOBJ' replacement, and the `fnmatch_.h'
file is linked to `fnmatch.h' so that it can be included in place
of the system `'.
This macro caches its result in the `ac_cv_func_fnmatch_works'
variable.
This macro is obsolescent, as it assumes the use of particular
source files. New programs should use Gnulib's `fnmatch-posix'
module, which provides this macro along with the source files.
*Note Gnulib::.
File: autoconf.info, Node: Generic Functions, Prev: Particular Functions, Up: Library Functions
5.5.3 Generic Function Checks
-----------------------------
These macros are used to find functions not covered by the "particular"
test macros. If the functions might be in libraries other than the
default C library, first call `AC_CHECK_LIB' for those libraries. If
you need to check the behavior of a function as well as find out
whether it is present, you have to write your own test for it (*note
Writing Tests::).
-- Macro: AC_CHECK_FUNC (FUNCTION, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
If C function FUNCTION is available, run shell commands
ACTION-IF-FOUND, otherwise ACTION-IF-NOT-FOUND. If you just want
to define a symbol if the function is available, consider using
`AC_CHECK_FUNCS' instead. This macro checks for functions with C
linkage even when `AC_LANG(C++)' has been called, since C is more
standardized than C++. (*note Language Choice::, for more
information about selecting the language for checks.)
This macro caches its result in the `ac_cv_func_FUNCTION' variable.
-- Macro: AC_CHECK_FUNCS (FUNCTION..., [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
For each FUNCTION enumerated in the blank-or-newline-separated
argument list, define `HAVE_FUNCTION' (in all capitals) if it is
available. If ACTION-IF-FOUND is given, it is additional shell
code to execute when one of the functions is found. You can give
it a value of `break' to break out of the loop on the first match.
If ACTION-IF-NOT-FOUND is given, it is executed when one of the
functions is not found.
Results are cached for each FUNCTION as in `AC_CHECK_FUNC'.
-- Macro: AC_CHECK_FUNCS_ONCE (FUNCTION...)
For each FUNCTION enumerated in the blank-or-newline-separated
argument list, define `HAVE_FUNCTION' (in all capitals) if it is
available. This is a once-only variant of `AC_CHECK_FUNCS'. It
generates the checking code at most once, so that `configure' is
smaller and faster; but the checks cannot be conditionalized and
are always done once, early during the `configure' run.
Autoconf follows a philosophy that was formed over the years by those
who have struggled for portability: isolate the portability issues in
specific files, and then program as if you were in a Posix environment.
Some functions may be missing or unfixable, and your package must be
ready to replace them.
Suitable replacements for many such problem functions are available
from Gnulib (*note Gnulib::).
-- Macro: AC_LIBOBJ (FUNCTION)
Specify that `FUNCTION.c' must be included in the executables to
replace a missing or broken implementation of FUNCTION.
Technically, it adds `FUNCTION.$ac_objext' to the output variable
`LIBOBJS' if it is not already in, and calls `AC_LIBSOURCE' for
`FUNCTION.c'. You should not directly change `LIBOBJS', since
this is not traceable.
-- Macro: AC_LIBSOURCE (FILE)
Specify that FILE might be needed to compile the project. If you
need to know what files might be needed by a `configure.ac', you
should trace `AC_LIBSOURCE'. FILE must be a literal.
This macro is called automatically from `AC_LIBOBJ', but you must
call it explicitly if you pass a shell variable to `AC_LIBOBJ'. In
that case, since shell variables cannot be traced statically, you
must pass to `AC_LIBSOURCE' any possible files that the shell
variable might cause `AC_LIBOBJ' to need. For example, if you
want to pass a variable `$foo_or_bar' to `AC_LIBOBJ' that holds
either `"foo"' or `"bar"', you should do:
AC_LIBSOURCE([foo.c])
AC_LIBSOURCE([bar.c])
AC_LIBOBJ([$foo_or_bar])
There is usually a way to avoid this, however, and you are
encouraged to simply call `AC_LIBOBJ' with literal arguments.
Note that this macro replaces the obsolete `AC_LIBOBJ_DECL', with
slightly different semantics: the old macro took the function name,
e.g., `foo', as its argument rather than the file name.
-- Macro: AC_LIBSOURCES (FILES)
Like `AC_LIBSOURCE', but accepts one or more FILES in a
comma-separated M4 list. Thus, the above example might be
rewritten:
AC_LIBSOURCES([foo.c, bar.c])
AC_LIBOBJ([$foo_or_bar])
-- Macro: AC_CONFIG_LIBOBJ_DIR (DIRECTORY)
Specify that `AC_LIBOBJ' replacement files are to be found in
DIRECTORY, a name relative to the top level of the source tree.
The replacement directory defaults to `.', the top level
directory, and the most typical value is `lib', corresponding to
`AC_CONFIG_LIBOBJ_DIR([lib])'.
`configure' might need to know the replacement directory for the
following reasons: (i) some checks use the replacement files, (ii)
some macros bypass broken system headers by installing links to the
replacement headers (iii) when used in conjunction with Automake,
within each makefile, DIRECTORY is used as a relative path from
`$(top_srcdir)' to each object named in `LIBOBJS' and `LTLIBOBJS',
etc.
It is common to merely check for the existence of a function, and ask
for its `AC_LIBOBJ' replacement if missing. The following macro is a
convenient shorthand.
-- Macro: AC_REPLACE_FUNCS (FUNCTION...)
Like `AC_CHECK_FUNCS', but uses `AC_LIBOBJ(FUNCTION)' as
ACTION-IF-NOT-FOUND. You can declare your replacement function by
enclosing the prototype in `#ifndef HAVE_FUNCTION'. If the system
has the function, it probably declares it in a header file you
should be including, so you shouldn't redeclare it lest your
declaration conflict.
File: autoconf.info, Node: Header Files, Next: Declarations, Prev: Library Functions, Up: Existing Tests
5.6 Header Files
================
The following macros check for the presence of certain C header files.
If there is no macro specifically defined to check for a header file
you need, and you don't need to check for any special properties of it,
then you can use one of the general header-file check macros.
* Menu:
* Header Portability:: Collected knowledge on common headers
* Particular Headers:: Special handling to find certain headers
* Generic Headers:: How to find other headers
File: autoconf.info, Node: Header Portability, Next: Particular Headers, Up: Header Files
5.6.1 Portability of Headers
----------------------------
This section documents some collected knowledge about common headers,
and the problems they cause. By definition, this list always requires
additions. A much more complete list is maintained by the Gnulib
project (*note Gnulib::), covering *note Posix Headers: (gnulib)Header
File Substitutes. and *note Glibc Headers: (gnulib)Glibc Header File
Substitutes. Please help us keep the gnulib list as complete as
possible.
`limits.h'
C99 says that `limits.h' defines `LLONG_MIN', `LLONG_MAX', and
`ULLONG_MAX', but many almost-C99 environments (e.g., default GCC
4.0.2 + glibc 2.4) do not define them.
`inttypes.h' vs. `stdint.h'
The C99 standard says that `inttypes.h' includes `stdint.h', so
there's no need to include `stdint.h' separately in a standard
environment. Some implementations have `inttypes.h' but not
`stdint.h' (e.g., Solaris 7), but we don't know of any
implementation that has `stdint.h' but not `inttypes.h'.
`linux/irda.h'
It requires `linux/types.h' and `sys/socket.h'.
`linux/random.h'
It requires `linux/types.h'.
`net/if.h'
On Darwin, this file requires that `sys/socket.h' be included
beforehand. One should run:
AC_CHECK_HEADERS([sys/socket.h])
AC_CHECK_HEADERS([net/if.h], [], [],
[#include
#ifdef STDC_HEADERS
# include
# include
#else
# ifdef HAVE_STDLIB_H
# include
# endif
#endif
#ifdef HAVE_SYS_SOCKET_H
# include
#endif
])
`netinet/if_ether.h'
On Darwin, this file requires that `stdio.h' and `sys/socket.h' be
included beforehand. One should run:
AC_CHECK_HEADERS([sys/socket.h])
AC_CHECK_HEADERS([netinet/if_ether.h], [], [],
[#include
#ifdef STDC_HEADERS
# include
# include
#else
# ifdef HAVE_STDLIB_H
# include
# endif
#endif
#ifdef HAVE_SYS_SOCKET_H
# include
#endif
])
`stdint.h'
See above, item `inttypes.h' vs. `stdint.h'.
`stdlib.h'
On many systems (e.g., Darwin), `stdio.h' is a prerequisite.
`sys/mount.h'
On FreeBSD 4.8 on ia32 and using gcc version 2.95.4,
`sys/params.h' is a prerequisite.
`sys/ptem.h'
On Solaris 8, `sys/stream.h' is a prerequisite.
`sys/socket.h'
On Darwin, `stdlib.h' is a prerequisite.
`sys/ucred.h'
On Tru64 5.1, `sys/types.h' is a prerequisite.
`X11/extensions/scrnsaver.h'
Using XFree86, this header requires `X11/Xlib.h', which is probably
so required that you might not even consider looking for it.
AC_CHECK_HEADERS([X11/extensions/scrnsaver.h], [], [],
[[#include
]])
File: autoconf.info, Node: Particular Headers, Next: Generic Headers, Prev: Header Portability, Up: Header Files
5.6.2 Particular Header Checks
------------------------------
These macros check for particular system header files--whether they
exist, and in some cases whether they declare certain symbols.
-- Macro: AC_CHECK_HEADER_STDBOOL
Check whether `stdbool.h' exists and conforms to C99, and cache the
result in the `ac_cv_header_stdbool_h' variable. If the type
`_Bool' is defined, define `HAVE__BOOL' to 1.
This macro is intended for use by Gnulib (*note Gnulib::) and other
packages that supply a substitute `stdbool.h' on platforms lacking
a conforming one. The `AC_HEADER_STDBOOL' macro is better for code
that explicitly checks for `stdbool.h'.
-- Macro: AC_HEADER_ASSERT
Check whether to enable assertions in the style of `assert.h'.
Assertions are enabled by default, but the user can override this
by invoking `configure' with the `--disable-assert' option.
-- Macro: AC_HEADER_DIRENT
Check for the following header files. For the first one that is
found and defines `DIR', define the listed C preprocessor macro:
`dirent.h' `HAVE_DIRENT_H'
`sys/ndir.h' `HAVE_SYS_NDIR_H'
`sys/dir.h' `HAVE_SYS_DIR_H'
`ndir.h' `HAVE_NDIR_H'
The directory-library declarations in your source code should look
something like the following:
#include
#ifdef HAVE_DIRENT_H
# include
# define NAMLEN(dirent) strlen ((dirent)->d_name)
#else
# define dirent direct
# define NAMLEN(dirent) ((dirent)->d_namlen)
# ifdef HAVE_SYS_NDIR_H
# include
# endif
# ifdef HAVE_SYS_DIR_H
# include
# endif
# ifdef HAVE_NDIR_H
# include
# endif
#endif
Using the above declarations, the program would declare variables
to be of type `struct dirent', not `struct direct', and would
access the length of a directory entry name by passing a pointer
to a `struct dirent' to the `NAMLEN' macro.
This macro also checks for the SCO Xenix `dir' and `x' libraries.
This macro is obsolescent, as all current systems with directory
libraries have `'. New programs need not use this macro.
Also see `AC_STRUCT_DIRENT_D_INO' and `AC_STRUCT_DIRENT_D_TYPE'
(*note Particular Structures::).
-- Macro: AC_HEADER_MAJOR
If `sys/types.h' does not define `major', `minor', and `makedev',
but `sys/mkdev.h' does, define `MAJOR_IN_MKDEV'; otherwise, if
`sys/sysmacros.h' does, define `MAJOR_IN_SYSMACROS'.
-- Macro: AC_HEADER_RESOLV
Checks for header `resolv.h', checking for prerequisites first.
To properly use `resolv.h', your code should contain something like
the following:
#ifdef HAVE_SYS_TYPES_H
# include
#endif
#ifdef HAVE_NETINET_IN_H
# include /* inet_ functions / structs */
#endif
#ifdef HAVE_ARPA_NAMESER_H
# include /* DNS HEADER struct */
#endif
#ifdef HAVE_NETDB_H
# include
#endif
#include
-- Macro: AC_HEADER_STAT
If the macros `S_ISDIR', `S_ISREG', etc. defined in `sys/stat.h'
do not work properly (returning false positives), define
`STAT_MACROS_BROKEN'. This is the case on Tektronix UTekV, Amdahl
UTS and Motorola System V/88.
This macro is obsolescent, as no current systems have the bug.
New programs need not use this macro.
-- Macro: AC_HEADER_STDBOOL
If `stdbool.h' exists and conforms to C99, define `HAVE_STDBOOL_H'
to 1; if the type `_Bool' is defined, define `HAVE__BOOL' to 1.
To fulfill the C99 requirements, your program could contain the
following code:
#ifdef HAVE_STDBOOL_H
# include
#else
# ifndef HAVE__BOOL
# ifdef __cplusplus
typedef bool _Bool;
# else
# define _Bool signed char
# endif
# endif
# define bool _Bool
# define false 0
# define true 1
# define __bool_true_false_are_defined 1
#endif
Alternatively you can use the `stdbool' package of Gnulib (*note
Gnulib::). It simplifies your code so that it can say just
`#include ', and it adds support for less-common
platforms.
This macro caches its result in the `ac_cv_header_stdbool_h'
variable.
This macro differs from `AC_CHECK_HEADER_STDBOOL' only in that it
defines `HAVE_STDBOOL_H' whereas `AC_CHECK_HEADER_STDBOOL' does
not.
-- Macro: AC_HEADER_STDC
Define `STDC_HEADERS' if the system has C header files conforming
to ANSI C89 (ISO C90). Specifically, this macro checks for
`stdlib.h', `stdarg.h', `string.h', and `float.h'; if the system
has those, it probably has the rest of the C89 header files. This
macro also checks whether `string.h' declares `memchr' (and thus
presumably the other `mem' functions), whether `stdlib.h' declare
`free' (and thus presumably `malloc' and other related functions),
and whether the `ctype.h' macros work on characters with the high
bit set, as the C standard requires.
If you use this macro, your code can refer to `STDC_HEADERS' to
determine whether the system has conforming header files (and
probably C library functions).
This macro caches its result in the `ac_cv_header_stdc' variable.
This macro is obsolescent, as current systems have conforming
header files. New programs need not use this macro.
Nowadays `string.h' is part of the C standard and declares
functions like `strcpy', and `strings.h' is standardized by Posix
and declares BSD functions like `bcopy'; but historically, string
functions were a major sticking point in this area. If you still
want to worry about portability to ancient systems without
standard headers, there is so much variation that it is probably
easier to declare the functions you use than to figure out exactly
what the system header files declare. Some ancient systems
contained a mix of functions from the C standard and from BSD;
some were mostly standard but lacked `memmove'; some defined the
BSD functions as macros in `string.h' or `strings.h'; some had
only the BSD functions but `string.h'; some declared the memory
functions in `memory.h', some in `string.h'; etc. It is probably
sufficient to check for one string function and one memory
function; if the library had the standard versions of those then
it probably had most of the others. If you put the following in
`configure.ac':
# This example is obsolescent.
# Nowadays you can omit these macro calls.
AC_HEADER_STDC
AC_CHECK_FUNCS([strchr memcpy])
then, in your code, you can use declarations like this:
/* This example is obsolescent.
Nowadays you can just #include . */
#ifdef STDC_HEADERS
# include
#else
# ifndef HAVE_STRCHR
# define strchr index
# define strrchr rindex
# endif
char *strchr (), *strrchr ();
# ifndef HAVE_MEMCPY
# define memcpy(d, s, n) bcopy ((s), (d), (n))
# define memmove(d, s, n) bcopy ((s), (d), (n))
# endif
#endif
If you use a function like `memchr', `memset', `strtok', or
`strspn', which have no BSD equivalent, then macros don't suffice
to port to ancient hosts; you must provide an implementation of
each function. An easy way to incorporate your implementations
only when needed (since the ones in system C libraries may be hand
optimized) is to, taking `memchr' for example, put it in
`memchr.c' and use `AC_REPLACE_FUNCS([memchr])'.
-- Macro: AC_HEADER_SYS_WAIT
If `sys/wait.h' exists and is compatible with Posix, define
`HAVE_SYS_WAIT_H'. Incompatibility can occur if `sys/wait.h' does
not exist, or if it uses the old BSD `union wait' instead of `int'
to store a status value. If `sys/wait.h' is not Posix compatible,
then instead of including it, define the Posix macros with their
usual interpretations. Here is an example:
#include
#ifdef HAVE_SYS_WAIT_H
# include
#endif
#ifndef WEXITSTATUS
# define WEXITSTATUS(stat_val) ((unsigned int) (stat_val) >> 8)
#endif
#ifndef WIFEXITED
# define WIFEXITED(stat_val) (((stat_val) & 255) == 0)
#endif
This macro caches its result in the `ac_cv_header_sys_wait_h'
variable.
This macro is obsolescent, as current systems are compatible with
Posix. New programs need not use this macro.
`_POSIX_VERSION' is defined when `unistd.h' is included on Posix
systems. If there is no `unistd.h', it is definitely not a Posix
system. However, some non-Posix systems do have `unistd.h'.
The way to check whether the system supports Posix is:
#ifdef HAVE_UNISTD_H
# include
# include
#endif
#ifdef _POSIX_VERSION
/* Code for Posix systems. */
#endif
-- Macro: AC_HEADER_TIME
If a program may include both `time.h' and `sys/time.h', define
`TIME_WITH_SYS_TIME'. On some ancient systems, `sys/time.h'
included `time.h', but `time.h' was not protected against multiple
inclusion, so programs could not explicitly include both files.
This macro is useful in programs that use, for example, `struct
timeval' as well as `struct tm'. It is best used in conjunction
with `HAVE_SYS_TIME_H', which can be checked for using
`AC_CHECK_HEADERS([sys/time.h])'.
#ifdef TIME_WITH_SYS_TIME
# include
# include
#else
# ifdef HAVE_SYS_TIME_H
# include
# else
# include
# endif
#endif
This macro caches its result in the `ac_cv_header_time' variable.
This macro is obsolescent, as current systems can include both
files when they exist. New programs need not use this macro.
-- Macro: AC_HEADER_TIOCGWINSZ
If the use of `TIOCGWINSZ' requires `', then define
`GWINSZ_IN_SYS_IOCTL'. Otherwise `TIOCGWINSZ' can be found in
`'.
Use:
#ifdef HAVE_TERMIOS_H
# include
#endif
#ifdef GWINSZ_IN_SYS_IOCTL
# include
#endif
File: autoconf.info, Node: Generic Headers, Prev: Particular Headers, Up: Header Files
5.6.3 Generic Header Checks
---------------------------
These macros are used to find system header files not covered by the
"particular" test macros. If you need to check the contents of a header
as well as find out whether it is present, you have to write your own
test for it (*note Writing Tests::).
-- Macro: AC_CHECK_HEADER (HEADER-FILE, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES])
If the system header file HEADER-FILE is compilable, execute shell
commands ACTION-IF-FOUND, otherwise execute ACTION-IF-NOT-FOUND.
If you just want to define a symbol if the header file is
available, consider using `AC_CHECK_HEADERS' instead.
INCLUDES is decoded to determine the appropriate include
directives. If omitted or empty, `configure' will check for both
header existence (with the preprocessor) and usability (with the
compiler), using `AC_INCLUDES_DEFAULT' for the compile test. If
there is a discrepancy between the results, a warning is issued to
the user, and the compiler results are favored (*note Present But
Cannot Be Compiled::). In general, favoring the compiler results
means that a header will be treated as not found even though the
file exists, because you did not provide enough prerequisites.
Providing a non-empty INCLUDES argument allows the code to provide
any prerequisites prior to including the header under test; it is
common to use the argument `AC_INCLUDES_DEFAULT' (*note Default
Includes::). With an explicit fourth argument, no preprocessor
test is needed. As a special case, an INCLUDES of exactly `-'
triggers the older preprocessor check, which merely determines
existence of the file in the preprocessor search path; this should
only be used as a last resort (it is safer to determine the actual
prerequisites and perform a compiler check, or else use
`AC_PREPROC_IFELSE' to make it obvious that only a preprocessor
check is desired).
This macro caches its result in the `ac_cv_header_HEADER-FILE'
variable, with characters not suitable for a variable name mapped
to underscores.
-- Macro: AC_CHECK_HEADERS (HEADER-FILE..., [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES])
For each given system header file HEADER-FILE in the
blank-separated argument list that exists, define
`HAVE_HEADER-FILE' (in all capitals). If ACTION-IF-FOUND is
given, it is additional shell code to execute when one of the
header files is found. You can give it a value of `break' to
break out of the loop on the first match. If ACTION-IF-NOT-FOUND
is given, it is executed when one of the header files is not found.
INCLUDES is interpreted as in `AC_CHECK_HEADER', in order to
choose the set of preprocessor directives supplied before the
header under test.
This macro caches its result in the `ac_cv_header_HEADER-FILE'
variable, with characters not suitable for a variable name mapped
to underscores.
Previous versions of Autoconf merely checked whether the header was
accepted by the preprocessor. This was changed because the old test was
inappropriate for typical uses. Headers are typically used to compile,
not merely to preprocess, and the old behavior sometimes accepted
headers that clashed at compile-time (*note Present But Cannot Be
Compiled::). If you need to check whether a header is preprocessable,
you can use `AC_PREPROC_IFELSE' (*note Running the Preprocessor::).
Actually requiring a header to compile improves the robustness of the
test, but it also requires that you make sure that headers that must be
included before the HEADER-FILE be part of the INCLUDES, (*note Default
Includes::). If looking for `bar.h', which requires that `foo.h' be
included before if it exists, we suggest the following scheme:
AC_CHECK_HEADERS([foo.h])
AC_CHECK_HEADERS([bar.h], [], [],
[#ifdef HAVE_FOO_H
# include
#endif
])
The following variant generates smaller, faster `configure' files if
you do not need the full power of `AC_CHECK_HEADERS'.
-- Macro: AC_CHECK_HEADERS_ONCE (HEADER-FILE...)
For each given system header file HEADER-FILE in the
blank-separated argument list that exists, define
`HAVE_HEADER-FILE' (in all capitals). This is a once-only variant
of `AC_CHECK_HEADERS'. It generates the checking code at most
once, so that `configure' is smaller and faster; but the checks
cannot be conditionalized and are always done once, early during
the `configure' run. Thus, this macro is only safe for checking
headers that do not have prerequisites beyond what
`AC_INCLUDES_DEFAULT' provides.
File: autoconf.info, Node: Declarations, Next: Structures, Prev: Header Files, Up: Existing Tests
5.7 Declarations
================
The following macros check for the declaration of variables and
functions. If there is no macro specifically defined to check for a
symbol you need, then you can use the general macros (*note Generic
Declarations::) or, for more complex tests, you may use
`AC_COMPILE_IFELSE' (*note Running the Compiler::).
* Menu:
* Particular Declarations:: Macros to check for certain declarations
* Generic Declarations:: How to find other declarations
File: autoconf.info, Node: Particular Declarations, Next: Generic Declarations, Up: Declarations
5.7.1 Particular Declaration Checks
-----------------------------------
There are no specific macros for declarations.
File: autoconf.info, Node: Generic Declarations, Prev: Particular Declarations, Up: Declarations
5.7.2 Generic Declaration Checks
--------------------------------
These macros are used to find declarations not covered by the
"particular" test macros.
-- Macro: AC_CHECK_DECL (SYMBOL, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `AC_INCLUDES_DEFAULT'])
If SYMBOL (a function, variable, or constant) is not declared in
INCLUDES and a declaration is needed, run the shell commands
ACTION-IF-NOT-FOUND, otherwise ACTION-IF-FOUND. INCLUDES is a
series of include directives, defaulting to `AC_INCLUDES_DEFAULT'
(*note Default Includes::), which are used prior to the
declaration under test.
This macro actually tests whether SYMBOL is defined as a macro or
can be used as an r-value, not whether it is really declared,
because it is much safer to avoid introducing extra declarations
when they are not needed. In order to facilitate use of C++ and
overloaded function declarations, it is possible to specify
function argument types in parentheses for types which can be
zero-initialized:
AC_CHECK_DECL([basename(char *)])
This macro caches its result in the `ac_cv_have_decl_SYMBOL'
variable, with characters not suitable for a variable name mapped
to underscores.
-- Macro: AC_CHECK_DECLS (SYMBOLS, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `AC_INCLUDES_DEFAULT'])
For each of the SYMBOLS (_comma_-separated list with optional
function argument types for C++ overloads), define
`HAVE_DECL_SYMBOL' (in all capitals) to `1' if SYMBOL is declared,
otherwise to `0'. If ACTION-IF-NOT-FOUND is given, it is
additional shell code to execute when one of the function
declarations is needed, otherwise ACTION-IF-FOUND is executed.
INCLUDES is a series of include directives, defaulting to
`AC_INCLUDES_DEFAULT' (*note Default Includes::), which are used
prior to the declarations under test.
This macro uses an M4 list as first argument:
AC_CHECK_DECLS([strdup])
AC_CHECK_DECLS([strlen])
AC_CHECK_DECLS([malloc, realloc, calloc, free])
AC_CHECK_DECLS([j0], [], [], [[#include ]])
AC_CHECK_DECLS([[basename(char *)], [dirname(char *)]])
Unlike the other `AC_CHECK_*S' macros, when a SYMBOL is not
declared, `HAVE_DECL_SYMBOL' is defined to `0' instead of leaving
`HAVE_DECL_SYMBOL' undeclared. When you are _sure_ that the check
was performed, use `HAVE_DECL_SYMBOL' in `#if':
#if !HAVE_DECL_SYMBOL
extern char *symbol;
#endif
If the test may have not been performed, however, because it is
safer _not_ to declare a symbol than to use a declaration that
conflicts with the system's one, you should use:
#if defined HAVE_DECL_MALLOC && !HAVE_DECL_MALLOC
void *malloc (size_t *s);
#endif
You fall into the second category only in extreme situations:
either your files may be used without being configured, or they
are used during the configuration. In most cases the traditional
approach is enough.
This macro caches its results in `ac_cv_have_decl_SYMBOL'
variables, with characters not suitable for a variable name mapped
to underscores.
-- Macro: AC_CHECK_DECLS_ONCE (SYMBOLS)
For each of the SYMBOLS (_comma_-separated list), define
`HAVE_DECL_SYMBOL' (in all capitals) to `1' if SYMBOL is declared
in the default include files, otherwise to `0'. This is a
once-only variant of `AC_CHECK_DECLS'. It generates the checking
code at most once, so that `configure' is smaller and faster; but
the checks cannot be conditionalized and are always done once,
early during the `configure' run.
File: autoconf.info, Node: Structures, Next: Types, Prev: Declarations, Up: Existing Tests
5.8 Structures
==============
The following macros check for the presence of certain members in C
structures. If there is no macro specifically defined to check for a
member you need, then you can use the general structure-member macros
(*note Generic Structures::) or, for more complex tests, you may use
`AC_COMPILE_IFELSE' (*note Running the Compiler::).
* Menu:
* Particular Structures:: Macros to check for certain structure members
* Generic Structures:: How to find other structure members
File: autoconf.info, Node: Particular Structures, Next: Generic Structures, Up: Structures
5.8.1 Particular Structure Checks
---------------------------------
The following macros check for certain structures or structure members.
-- Macro: AC_STRUCT_DIRENT_D_INO
Perform all the actions of `AC_HEADER_DIRENT' (*note Particular
Headers::). Then, if `struct dirent' contains a `d_ino' member,
define `HAVE_STRUCT_DIRENT_D_INO'.
`HAVE_STRUCT_DIRENT_D_INO' indicates only the presence of `d_ino',
not whether its contents are always reliable. Traditionally, a
zero `d_ino' indicated a deleted directory entry, though current
systems hide this detail from the user and never return zero
`d_ino' values. Many current systems report an incorrect `d_ino'
for a directory entry that is a mount point.
-- Macro: AC_STRUCT_DIRENT_D_TYPE
Perform all the actions of `AC_HEADER_DIRENT' (*note Particular
Headers::). Then, if `struct dirent' contains a `d_type' member,
define `HAVE_STRUCT_DIRENT_D_TYPE'.
-- Macro: AC_STRUCT_ST_BLOCKS
If `struct stat' contains an `st_blocks' member, define
`HAVE_STRUCT_STAT_ST_BLOCKS'. Otherwise, require an `AC_LIBOBJ'
replacement of `fileblocks'. The former name, `HAVE_ST_BLOCKS' is
to be avoided, as its support will cease in the future.
This macro caches its result in the
`ac_cv_member_struct_stat_st_blocks' variable.
-- Macro: AC_STRUCT_TM
If `time.h' does not define `struct tm', define `TM_IN_SYS_TIME',
which means that including `sys/time.h' had better define `struct
tm'.
This macro is obsolescent, as `time.h' defines `struct tm' in
current systems. New programs need not use this macro.
-- Macro: AC_STRUCT_TIMEZONE
Figure out how to get the current timezone. If `struct tm' has a
`tm_zone' member, define `HAVE_STRUCT_TM_TM_ZONE' (and the
obsoleted `HAVE_TM_ZONE'). Otherwise, if the external array
`tzname' is found, define `HAVE_TZNAME'; if it is declared, define
`HAVE_DECL_TZNAME'.
File: autoconf.info, Node: Generic Structures, Prev: Particular Structures, Up: Structures
5.8.2 Generic Structure Checks
------------------------------
These macros are used to find structure members not covered by the
"particular" test macros.
-- Macro: AC_CHECK_MEMBER (AGGREGATE.MEMBER, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `AC_INCLUDES_DEFAULT'])
Check whether MEMBER is a member of the aggregate AGGREGATE. If
no INCLUDES are specified, the default includes are used (*note
Default Includes::).
AC_CHECK_MEMBER([struct passwd.pw_gecos], [],
[AC_MSG_ERROR([we need `passwd.pw_gecos'])],
[[#include ]])
You can use this macro for submembers:
AC_CHECK_MEMBER(struct top.middle.bot)
This macro caches its result in the
`ac_cv_member_AGGREGATE_MEMBER' variable, with characters not
suitable for a variable name mapped to underscores.
-- Macro: AC_CHECK_MEMBERS (MEMBERS, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `AC_INCLUDES_DEFAULT'])
Check for the existence of each `AGGREGATE.MEMBER' of MEMBERS
using the previous macro. When MEMBER belongs to AGGREGATE,
define `HAVE_AGGREGATE_MEMBER' (in all capitals, with spaces and
dots replaced by underscores). If ACTION-IF-FOUND is given, it is
executed for each of the found members. If ACTION-IF-NOT-FOUND is
given, it is executed for each of the members that could not be
found.
INCLUDES is a series of include directives, defaulting to
`AC_INCLUDES_DEFAULT' (*note Default Includes::), which are used
prior to the members under test.
This macro uses M4 lists:
AC_CHECK_MEMBERS([struct stat.st_rdev, struct stat.st_blksize])
File: autoconf.info, Node: Types, Next: Compilers and Preprocessors, Prev: Structures, Up: Existing Tests
5.9 Types
=========
The following macros check for C types, either builtin or typedefs. If
there is no macro specifically defined to check for a type you need, and
you don't need to check for any special properties of it, then you can
use a general type-check macro.
* Menu:
* Particular Types:: Special handling to find certain types
* Generic Types:: How to find other types
File: autoconf.info, Node: Particular Types, Next: Generic Types, Up: Types
5.9.1 Particular Type Checks
----------------------------
These macros check for particular C types in `sys/types.h', `stdlib.h',
`stdint.h', `inttypes.h' and others, if they exist.
The Gnulib `stdint' module is an alternate way to define many of
these symbols; it is useful if you prefer your code to assume a
C99-or-better environment. *Note Gnulib::.
-- Macro: AC_TYPE_GETGROUPS
Define `GETGROUPS_T' to be whichever of `gid_t' or `int' is the
base type of the array argument to `getgroups'.
This macro caches the base type in the `ac_cv_type_getgroups'
variable.
-- Macro: AC_TYPE_INT8_T
If `stdint.h' or `inttypes.h' does not define the type `int8_t',
define `int8_t' to a signed integer type that is exactly 8 bits
wide and that uses two's complement representation, if such a type
exists. If you are worried about porting to hosts that lack such
a type, you can use the results of this macro in C89-or-later code
as follows:
#if HAVE_STDINT_H
# include
#endif
#if defined INT8_MAX || defined int8_t
_code using int8_t_
#else
_complicated alternative using >8-bit 'signed char'_
#endif
This macro caches the type in the `ac_cv_c_int8_t' variable.
-- Macro: AC_TYPE_INT16_T
This is like `AC_TYPE_INT8_T', except for 16-bit integers.
-- Macro: AC_TYPE_INT32_T
This is like `AC_TYPE_INT8_T', except for 32-bit integers.
-- Macro: AC_TYPE_INT64_T
This is like `AC_TYPE_INT8_T', except for 64-bit integers.
-- Macro: AC_TYPE_INTMAX_T
If `stdint.h' or `inttypes.h' defines the type `intmax_t', define
`HAVE_INTMAX_T'. Otherwise, define `intmax_t' to the widest
signed integer type.
-- Macro: AC_TYPE_INTPTR_T
If `stdint.h' or `inttypes.h' defines the type `intptr_t', define
`HAVE_INTPTR_T'. Otherwise, define `intptr_t' to a signed integer
type wide enough to hold a pointer, if such a type exists.
-- Macro: AC_TYPE_LONG_DOUBLE
If the C compiler supports a working `long double' type, define
`HAVE_LONG_DOUBLE'. The `long double' type might have the same
range and precision as `double'.
This macro caches its result in the `ac_cv_type_long_double'
variable.
This macro is obsolescent, as current C compilers support `long
double'. New programs need not use this macro.
-- Macro: AC_TYPE_LONG_DOUBLE_WIDER
If the C compiler supports a working `long double' type with more
range or precision than the `double' type, define
`HAVE_LONG_DOUBLE_WIDER'.
This macro caches its result in the `ac_cv_type_long_double_wider'
variable.
-- Macro: AC_TYPE_LONG_LONG_INT
If the C compiler supports a working `long long int' type, define
`HAVE_LONG_LONG_INT'. However, this test does not test `long long
int' values in preprocessor `#if' expressions, because too many
compilers mishandle such expressions. *Note Preprocessor
Arithmetic::.
This macro caches its result in the `ac_cv_type_long_long_int'
variable.
-- Macro: AC_TYPE_MBSTATE_T
Define `HAVE_MBSTATE_T' if `' declares the `mbstate_t'
type. Also, define `mbstate_t' to be a type if `' does
not declare it.
This macro caches its result in the `ac_cv_type_mbstate_t'
variable.
-- Macro: AC_TYPE_MODE_T
Define `mode_t' to a suitable type, if standard headers do not
define it.
This macro caches its result in the `ac_cv_type_mode_t' variable.
-- Macro: AC_TYPE_OFF_T
Define `off_t' to a suitable type, if standard headers do not
define it.
This macro caches its result in the `ac_cv_type_off_t' variable.
-- Macro: AC_TYPE_PID_T
Define `pid_t' to a suitable type, if standard headers do not
define it.
This macro caches its result in the `ac_cv_type_pid_t' variable.
-- Macro: AC_TYPE_SIZE_T
Define `size_t' to a suitable type, if standard headers do not
define it.
This macro caches its result in the `ac_cv_type_size_t' variable.
-- Macro: AC_TYPE_SSIZE_T
Define `ssize_t' to a suitable type, if standard headers do not
define it.
This macro caches its result in the `ac_cv_type_ssize_t' variable.
-- Macro: AC_TYPE_UID_T
Define `uid_t' and `gid_t' to suitable types, if standard headers
do not define them.
This macro caches its result in the `ac_cv_type_uid_t' variable.
-- Macro: AC_TYPE_UINT8_T
If `stdint.h' or `inttypes.h' does not define the type `uint8_t',
define `uint8_t' to an unsigned integer type that is exactly 8
bits wide, if such a type exists. This is like `AC_TYPE_INT8_T',
except for unsigned integers.
-- Macro: AC_TYPE_UINT16_T
This is like `AC_TYPE_UINT8_T', except for 16-bit integers.
-- Macro: AC_TYPE_UINT32_T
This is like `AC_TYPE_UINT8_T', except for 32-bit integers.
-- Macro: AC_TYPE_UINT64_T
This is like `AC_TYPE_UINT8_T', except for 64-bit integers.
-- Macro: AC_TYPE_UINTMAX_T
If `stdint.h' or `inttypes.h' defines the type `uintmax_t', define
`HAVE_UINTMAX_T'. Otherwise, define `uintmax_t' to the widest
unsigned integer type.
-- Macro: AC_TYPE_UINTPTR_T
If `stdint.h' or `inttypes.h' defines the type `uintptr_t', define
`HAVE_UINTPTR_T'. Otherwise, define `uintptr_t' to an unsigned
integer type wide enough to hold a pointer, if such a type exists.
-- Macro: AC_TYPE_UNSIGNED_LONG_LONG_INT
If the C compiler supports a working `unsigned long long int' type,
define `HAVE_UNSIGNED_LONG_LONG_INT'. However, this test does not
test `unsigned long long int' values in preprocessor `#if'
expressions, because too many compilers mishandle such expressions.
*Note Preprocessor Arithmetic::.
This macro caches its result in the
`ac_cv_type_unsigned_long_long_int' variable.
File: autoconf.info, Node: Generic Types, Prev: Particular Types, Up: Types
5.9.2 Generic Type Checks
-------------------------
These macros are used to check for types not covered by the "particular"
test macros.
-- Macro: AC_CHECK_TYPE (TYPE, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `AC_INCLUDES_DEFAULT'])
Check whether TYPE is defined. It may be a compiler builtin type
or defined by the INCLUDES. INCLUDES is a series of include
directives, defaulting to `AC_INCLUDES_DEFAULT' (*note Default
Includes::), which are used prior to the type under test.
In C, TYPE must be a type-name, so that the expression `sizeof
(TYPE)' is valid (but `sizeof ((TYPE))' is not). The same test is
applied when compiling for C++, which means that in C++ TYPE
should be a type-id and should not be an anonymous `struct' or
`union'.
This macro caches its result in the `ac_cv_type_TYPE' variable,
with `*' mapped to `p' and other characters not suitable for a
variable name mapped to underscores.
-- Macro: AC_CHECK_TYPES (TYPES, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `AC_INCLUDES_DEFAULT'])
For each TYPE of the TYPES that is defined, define `HAVE_TYPE' (in
all capitals). Each TYPE must follow the rules of
`AC_CHECK_TYPE'. If no INCLUDES are specified, the default
includes are used (*note Default Includes::). If ACTION-IF-FOUND
is given, it is additional shell code to execute when one of the
types is found. If ACTION-IF-NOT-FOUND is given, it is executed
when one of the types is not found.
This macro uses M4 lists:
AC_CHECK_TYPES([ptrdiff_t])
AC_CHECK_TYPES([unsigned long long int, uintmax_t])
AC_CHECK_TYPES([float_t], [], [], [[#include ]])
Autoconf, up to 2.13, used to provide to another version of
`AC_CHECK_TYPE', broken by design. In order to keep backward
compatibility, a simple heuristic, quite safe but not totally, is
implemented. In case of doubt, read the documentation of the former
`AC_CHECK_TYPE', see *note Obsolete Macros::.
File: autoconf.info, Node: Compilers and Preprocessors, Next: System Services, Prev: Types, Up: Existing Tests
5.10 Compilers and Preprocessors
================================
All the tests for compilers (`AC_PROG_CC', `AC_PROG_CXX',
`AC_PROG_F77') define the output variable `EXEEXT' based on the output
of the compiler, typically to the empty string if Posix and `.exe' if a
DOS variant.
They also define the output variable `OBJEXT' based on the output of
the compiler, after `.c' files have been excluded, typically to `o' if
Posix, `obj' if a DOS variant.
If the compiler being used does not produce executables, the tests
fail. If the executables can't be run, and cross-compilation is not
enabled, they fail too. *Note Manual Configuration::, for more on
support for cross compiling.
* Menu:
* Specific Compiler Characteristics:: Some portability issues
* Generic Compiler Characteristics:: Language independent tests and features
* C Compiler:: Checking its characteristics
* C++ Compiler:: Likewise
* Objective C Compiler:: Likewise
* Objective C++ Compiler:: Likewise
* Erlang Compiler and Interpreter:: Likewise
* Fortran Compiler:: Likewise
* Go Compiler:: Likewise
File: autoconf.info, Node: Specific Compiler Characteristics, Next: Generic Compiler Characteristics, Up: Compilers and Preprocessors
5.10.1 Specific Compiler Characteristics
----------------------------------------
Some compilers exhibit different behaviors.
Static/Dynamic Expressions
Autoconf relies on a trick to extract one bit of information from
the C compiler: using negative array sizes. For instance the
following excerpt of a C source demonstrates how to test whether
`int' objects are 4 bytes wide:
static int test_array[sizeof (int) == 4 ? 1 : -1];
To our knowledge, there is a single compiler that does not support
this trick: the HP C compilers (the real ones, not only the
"bundled") on HP-UX 11.00. They incorrectly reject the above
program with the diagnostic "Variable-length arrays cannot have
static storage." This bug comes from HP compilers' mishandling of
`sizeof (int)', not from the `? 1 : -1', and Autoconf works around
this problem by casting `sizeof (int)' to `long int' before
comparing it.
File: autoconf.info, Node: Generic Compiler Characteristics, Next: C Compiler, Prev: Specific Compiler Characteristics, Up: Compilers and Preprocessors
5.10.2 Generic Compiler Characteristics
---------------------------------------
-- Macro: AC_CHECK_SIZEOF (TYPE-OR-EXPR, [UNUSED], [INCLUDES =
`AC_INCLUDES_DEFAULT'])
Define `SIZEOF_TYPE-OR-EXPR' (*note Standard Symbols::) to be the
size in bytes of TYPE-OR-EXPR, which may be either a type or an
expression returning a value that has a size. If the expression
`sizeof (TYPE-OR-EXPR)' is invalid, the result is 0. INCLUDES is
a series of include directives, defaulting to
`AC_INCLUDES_DEFAULT' (*note Default Includes::), which are used
prior to the expression under test.
This macro now works even when cross-compiling. The UNUSED
argument was used when cross-compiling.
For example, the call
AC_CHECK_SIZEOF([int *])
defines `SIZEOF_INT_P' to be 8 on DEC Alpha AXP systems.
This macro caches its result in the `ac_cv_sizeof_TYPE-OR-EXPR'
variable, with `*' mapped to `p' and other characters not suitable
for a variable name mapped to underscores.
-- Macro: AC_CHECK_ALIGNOF (TYPE, [INCLUDES = `AC_INCLUDES_DEFAULT'])
Define `ALIGNOF_TYPE' (*note Standard Symbols::) to be the
alignment in bytes of TYPE. `TYPE y;' must be valid as a
structure member declaration. If `type' is unknown, the result is
0. If no INCLUDES are specified, the default includes are used
(*note Default Includes::).
This macro caches its result in the `ac_cv_alignof_TYPE-OR-EXPR'
variable, with `*' mapped to `p' and other characters not suitable
for a variable name mapped to underscores.
-- Macro: AC_COMPUTE_INT (VAR, EXPRESSION, [INCLUDES =
`AC_INCLUDES_DEFAULT'], [ACTION-IF-FAILS])
Store into the shell variable VAR the value of the integer
EXPRESSION. The value should fit in an initializer in a C
variable of type `signed long'. To support cross compilation (in
which case, the macro only works on hosts that use twos-complement
arithmetic), it should be possible to evaluate the expression at
compile-time. If no INCLUDES are specified, the default includes
are used (*note Default Includes::).
Execute ACTION-IF-FAILS if the value cannot be determined
correctly.
-- Macro: AC_LANG_WERROR
Normally Autoconf ignores warnings generated by the compiler,
linker, and preprocessor. If this macro is used, warnings count
as fatal errors for the current language. This macro is useful
when the results of configuration are used where warnings are
unacceptable; for instance, if parts of a program are built with
the GCC `-Werror' option. If the whole program is built using
`-Werror' it is often simpler to put `-Werror' in the compiler
flags (`CFLAGS', etc.).
-- Macro: AC_OPENMP
OpenMP (http://www.openmp.org/) specifies extensions of C, C++,
and Fortran that simplify optimization of shared memory
parallelism, which is a common problem on multicore CPUs.
If the current language is C, the macro `AC_OPENMP' sets the
variable `OPENMP_CFLAGS' to the C compiler flags needed for
supporting OpenMP. `OPENMP_CFLAGS' is set to empty if the
compiler already supports OpenMP, if it has no way to activate
OpenMP support, or if the user rejects OpenMP support by invoking
`configure' with the `--disable-openmp' option.
`OPENMP_CFLAGS' needs to be used when compiling programs, when
preprocessing program source, and when linking programs.
Therefore you need to add `$(OPENMP_CFLAGS)' to the `CFLAGS' of C
programs that use OpenMP. If you preprocess OpenMP-specific C
code, you also need to add `$(OPENMP_CFLAGS)' to `CPPFLAGS'. The
presence of OpenMP support is revealed at compile time by the
preprocessor macro `_OPENMP'.
Linking a program with `OPENMP_CFLAGS' typically adds one more
shared library to the program's dependencies, so its use is
recommended only on programs that actually require OpenMP.
If the current language is C++, `AC_OPENMP' sets the variable
`OPENMP_CXXFLAGS', suitably for the C++ compiler. The same remarks
hold as for C.
If the current language is Fortran 77 or Fortran, `AC_OPENMP' sets
the variable `OPENMP_FFLAGS' or `OPENMP_FCFLAGS', respectively.
Similar remarks as for C hold, except that `CPPFLAGS' is not used
for Fortran, and no preprocessor macro signals OpenMP support.
For portability, it is best to avoid spaces between `#' and
`pragma omp'. That is, write `#pragma omp', not `# pragma omp'.
The Sun WorkShop 6.2 C compiler chokes on the latter.
This macro caches its result in the `ac_cv_prog_c_openmp',
`ac_cv_prog_cxx_openmp', `ac_cv_prog_f77_openmp', or
`ac_cv_prog_fc_openmp' variable, depending on the current language.
File: autoconf.info, Node: C Compiler, Next: C++ Compiler, Prev: Generic Compiler Characteristics, Up: Compilers and Preprocessors
5.10.3 C Compiler Characteristics
---------------------------------
The following macros provide ways to find and exercise a C Compiler.
There are a few constructs that ought to be avoided, but do not deserve
being checked for, since they can easily be worked around.
Don't use lines containing solitary backslashes
They tickle a bug in the HP-UX C compiler (checked on HP-UX 10.20,
11.00, and 11i). When given the following source:
#ifdef __STDC__
/\
* A comment with backslash-newlines in it. %{ %} *\
\
/
char str[] = "\\
" A string with backslash-newlines in it %{ %} \\
"";
char apostrophe = '\\
\
'\
';
#endif
the compiler incorrectly fails with the diagnostics
"Non-terminating comment at end of file" and "Missing `#endif' at
end of file." Removing the lines with solitary backslashes solves
the problem.
Don't compile several files at once if output matters to you
Some compilers, such as HP's, report names of files being compiled
when given more than one file operand. For instance:
$ cc a.c b.c
a.c:
b.c:
This can cause problems if you observe the output of the compiler
to detect failures. Invoking `cc -c a.c && cc -c b.c && cc -o c
a.o b.o' solves the issue.
Don't rely on `#error' failing
The IRIX C compiler does not fail when #error is preprocessed; it
simply emits a diagnostic and continues, exiting successfully. So,
instead of an error directive like `#error "Unsupported word size"'
it is more portable to use an invalid directive like `#Unsupported
word size' in Autoconf tests. In ordinary source code, `#error' is
OK, since installers with inadequate compilers like IRIX can simply
examine these compilers' diagnostic output.
Don't rely on correct `#line' support
On Solaris, `c89' (at least Sun C 5.3 through 5.8) diagnoses
`#line' directives whose line numbers are greater than 32767.
Nothing in Posix makes this invalid. That is why Autoconf stopped
issuing `#line' directives.
-- Macro: AC_PROG_CC ([COMPILER-SEARCH-LIST])
Determine a C compiler to use. If `CC' is not already set in the
environment, check for `gcc' and `cc', then for other C compilers.
Set output variable `CC' to the name of the compiler found.
This macro may, however, be invoked with an optional first argument
which, if specified, must be a blank-separated list of C compilers
to search for. This just gives the user an opportunity to specify
an alternative search list for the C compiler. For example, if
you didn't like the default order, then you could invoke
`AC_PROG_CC' like this:
AC_PROG_CC([gcc cl cc])
If the C compiler does not handle function prototypes correctly by
default, try to add an option to output variable `CC' to make it
so. This macro tries various options that select
standard-conformance modes on various systems.
After calling this macro you can check whether the C compiler has
been set to accept ANSI C89 (ISO C90); if not, the shell variable
`ac_cv_prog_cc_c89' is set to `no'. See also `AC_C_PROTOTYPES'
below.
If using the GNU C compiler, set shell variable `GCC' to `yes'.
If output variable `CFLAGS' was not already set, set it to `-g
-O2' for the GNU C compiler (`-O2' on systems where GCC does not
accept `-g'), or `-g' for other compilers. If your package does
not like this default, then it is acceptable to insert the line `:
${CFLAGS=""}' after `AC_INIT' and before `AC_PROG_CC' to select an
empty default instead.
Many Autoconf macros use a compiler, and thus call
`AC_REQUIRE([AC_PROG_CC])' to ensure that the compiler has been
determined before the body of the outermost `AC_DEFUN' macro.
Although `AC_PROG_CC' is safe to directly expand multiple times, it
performs certain checks (such as the proper value of `EXEEXT') only
on the first invocation. Therefore, care must be used when
invoking this macro from within another macro rather than at the
top level (*note Expanded Before Required::).
-- Macro: AC_PROG_CC_C_O
If the C compiler does not accept the `-c' and `-o' options
simultaneously, define `NO_MINUS_C_MINUS_O'. This macro actually
tests both the compiler found by `AC_PROG_CC', and, if different,
the first `cc' in the path. The test fails if one fails. This
macro was created for GNU Make to choose the default C compilation
rule.
For the compiler COMPILER, this macro caches its result in the
`ac_cv_prog_cc_COMPILER_c_o' variable.
-- Macro: AC_PROG_CPP
Set output variable `CPP' to a command that runs the C
preprocessor. If `$CC -E' doesn't work, `/lib/cpp' is used. It
is only portable to run `CPP' on files with a `.c' extension.
Some preprocessors don't indicate missing include files by the
error status. For such preprocessors an internal variable is set
that causes other macros to check the standard error from the
preprocessor and consider the test failed if any warnings have
been reported. For most preprocessors, though, warnings do not
cause include-file tests to fail unless `AC_PROG_CPP_WERROR' is
also specified.
-- Macro: AC_PROG_CPP_WERROR
This acts like `AC_PROG_CPP', except it treats warnings from the
preprocessor as errors even if the preprocessor exit status
indicates success. This is useful for avoiding headers that
generate mandatory warnings, such as deprecation notices.
The following macros check for C compiler or machine architecture
features. To check for characteristics not listed here, use
`AC_COMPILE_IFELSE' (*note Running the Compiler::) or `AC_RUN_IFELSE'
(*note Runtime::).
-- Macro: AC_PROG_CC_STDC
If the C compiler cannot compile ISO Standard C (currently C99),
try to add an option to output variable `CC' to make it work. If
the compiler does not support C99, fall back to supporting ANSI
C89 (ISO C90).
After calling this macro you can check whether the C compiler has
been set to accept Standard C; if not, the shell variable
`ac_cv_prog_cc_stdc' is set to `no'.
-- Macro: AC_PROG_CC_C89
If the C compiler is not in ANSI C89 (ISO C90) mode by default,
try to add an option to output variable `CC' to make it so. This
macro tries various options that select ANSI C89 on some system or
another, preferring extended functionality modes over strict
conformance modes. It considers the compiler to be in ANSI C89
mode if it handles function prototypes correctly.
After calling this macro you can check whether the C compiler has
been set to accept ANSI C89; if not, the shell variable
`ac_cv_prog_cc_c89' is set to `no'.
This macro is called automatically by `AC_PROG_CC'.
-- Macro: AC_PROG_CC_C99
If the C compiler is not in C99 mode by default, try to add an
option to output variable `CC' to make it so. This macro tries
various options that select C99 on some system or another,
preferring extended functionality modes over strict conformance
modes. It considers the compiler to be in C99 mode if it handles
`_Bool', `//' comments, flexible array members, `inline', signed
and unsigned `long long int', mixed code and declarations, named
initialization of structs, `restrict', `va_copy', varargs macros,
variable declarations in `for' loops, and variable length arrays.
After calling this macro you can check whether the C compiler has
been set to accept C99; if not, the shell variable
`ac_cv_prog_cc_c99' is set to `no'.
-- Macro: AC_C_BACKSLASH_A
Define `HAVE_C_BACKSLASH_A' to 1 if the C compiler understands
`\a'.
This macro is obsolescent, as current C compilers understand `\a'.
New programs need not use this macro.
-- Macro: AC_C_BIGENDIAN ([ACTION-IF-TRUE], [ACTION-IF-FALSE],
[ACTION-IF-UNKNOWN], [ACTION-IF-UNIVERSAL])
If words are stored with the most significant byte first (like
Motorola and SPARC CPUs), execute ACTION-IF-TRUE. If words are
stored with the least significant byte first (like Intel and VAX
CPUs), execute ACTION-IF-FALSE.
This macro runs a test-case if endianness cannot be determined
from the system header files. When cross-compiling, the test-case
is not run but grep'ed for some magic values. ACTION-IF-UNKNOWN
is executed if the latter case fails to determine the byte sex of
the host system.
In some cases a single run of a compiler can generate code for
multiple architectures. This can happen, for example, when
generating Mac OS X universal binary files, which work on both
PowerPC and Intel architectures. In this case, the different
variants might be for different architectures whose endiannesses
differ. If `configure' detects this, it executes
ACTION-IF-UNIVERSAL instead of ACTION-IF-UNKNOWN.
The default for ACTION-IF-TRUE is to define `WORDS_BIGENDIAN'.
The default for ACTION-IF-FALSE is to do nothing. The default for
ACTION-IF-UNKNOWN is to abort configure and tell the installer how
to bypass this test. And finally, the default for
ACTION-IF-UNIVERSAL is to ensure that `WORDS_BIGENDIAN' is defined
if and only if a universal build is detected and the current code
is big-endian; this default works only if `autoheader' is used
(*note autoheader Invocation::).
If you use this macro without specifying ACTION-IF-UNIVERSAL, you
should also use `AC_CONFIG_HEADERS'; otherwise `WORDS_BIGENDIAN'
may be set incorrectly for Mac OS X universal binary files.
-- Macro: AC_C_CONST
If the C compiler does not fully support the `const' keyword,
define `const' to be empty. Some C compilers that do not define
`__STDC__' do support `const'; some compilers that define
`__STDC__' do not completely support `const'. Programs can simply
use `const' as if every C compiler supported it; for those that
don't, the makefile or configuration header file defines it as
empty.
Occasionally installers use a C++ compiler to compile C code,
typically because they lack a C compiler. This causes problems
with `const', because C and C++ treat `const' differently. For
example:
const int foo;
is valid in C but not in C++. These differences unfortunately
cannot be papered over by defining `const' to be empty.
If `autoconf' detects this situation, it leaves `const' alone, as
this generally yields better results in practice. However, using a
C++ compiler to compile C code is not recommended or supported, and
installers who run into trouble in this area should get a C
compiler like GCC to compile their C code.
This macro caches its result in the `ac_cv_c_const' variable.
This macro is obsolescent, as current C compilers support `const'.
New programs need not use this macro.
-- Macro: AC_C_RESTRICT
If the C compiler recognizes a variant spelling for the `restrict'
keyword (`__restrict', `__restrict__', or `_Restrict'), then
define `restrict' to that; this is more likely to do the right
thing with compilers that support language variants where plain
`restrict' is not a keyword. Otherwise, if the C compiler
recognizes the `restrict' keyword, don't do anything. Otherwise,
define `restrict' to be empty. Thus, programs may simply use
`restrict' as if every C compiler supported it; for those that do
not, the makefile or configuration header defines it away.
Although support in C++ for the `restrict' keyword is not
required, several C++ compilers do accept the keyword. This macro
works for them, too.
This macro caches `no' in the `ac_cv_c_restrict' variable if
`restrict' is not supported, and a supported spelling otherwise.
-- Macro: AC_C_VOLATILE
If the C compiler does not understand the keyword `volatile',
define `volatile' to be empty. Programs can simply use `volatile'
as if every C compiler supported it; for those that do not, the
makefile or configuration header defines it as empty.
If the correctness of your program depends on the semantics of
`volatile', simply defining it to be empty does, in a sense, break
your code. However, given that the compiler does not support
`volatile', you are at its mercy anyway. At least your program
compiles, when it wouldn't before. *Note Volatile Objects::, for
more about `volatile'.
In general, the `volatile' keyword is a standard C feature, so you
might expect that `volatile' is available only when `__STDC__' is
defined. However, Ultrix 4.3's native compiler does support
volatile, but does not define `__STDC__'.
This macro is obsolescent, as current C compilers support
`volatile'. New programs need not use this macro.
-- Macro: AC_C_INLINE
If the C compiler supports the keyword `inline', do nothing.
Otherwise define `inline' to `__inline__' or `__inline' if it
accepts one of those, otherwise define `inline' to be empty.
-- Macro: AC_C_CHAR_UNSIGNED
If the C type `char' is unsigned, define `__CHAR_UNSIGNED__',
unless the C compiler predefines it.
These days, using this macro is not necessary. The same
information can be determined by this portable alternative, thus
avoiding the use of preprocessor macros in the namespace reserved
for the implementation.
#include
#if CHAR_MIN == 0
# define CHAR_UNSIGNED 1
#endif
-- Macro: AC_C_STRINGIZE
If the C preprocessor supports the stringizing operator, define
`HAVE_STRINGIZE'. The stringizing operator is `#' and is found in
macros such as this:
#define x(y) #y
This macro is obsolescent, as current C compilers support the
stringizing operator. New programs need not use this macro.
-- Macro: AC_C_FLEXIBLE_ARRAY_MEMBER
If the C compiler supports flexible array members, define
`FLEXIBLE_ARRAY_MEMBER' to nothing; otherwise define it to 1.
That way, a declaration like this:
struct s
{
size_t n_vals;
double val[FLEXIBLE_ARRAY_MEMBER];
};
will let applications use the "struct hack" even with compilers
that do not support flexible array members. To allocate and use
such an object, you can use code like this:
size_t i;
size_t n = compute_value_count ();
struct s *p =
malloc (offsetof (struct s, val)
+ n * sizeof (double));
p->n_vals = n;
for (i = 0; i < n; i++)
p->val[i] = compute_value (i);
-- Macro: AC_C_VARARRAYS
If the C compiler supports variable-length arrays, define
`HAVE_C_VARARRAYS'. A variable-length array is an array of
automatic storage duration whose length is determined at run time,
when the array is declared.
-- Macro: AC_C_TYPEOF
If the C compiler supports GCC's `typeof' syntax either directly or
through a different spelling of the keyword (e.g., `__typeof__'),
define `HAVE_TYPEOF'. If the support is available only through a
different spelling, define `typeof' to that spelling.
-- Macro: AC_C_PROTOTYPES
If function prototypes are understood by the compiler (as
determined by `AC_PROG_CC'), define `PROTOTYPES' and
`__PROTOTYPES'. Defining `__PROTOTYPES' is for the benefit of
header files that cannot use macros that infringe on user name
space.
This macro is obsolescent, as current C compilers support
prototypes. New programs need not use this macro.
-- Macro: AC_PROG_GCC_TRADITIONAL
Add `-traditional' to output variable `CC' if using the GNU C
compiler and `ioctl' does not work properly without
`-traditional'. That usually happens when the fixed header files
have not been installed on an old system.
This macro is obsolescent, since current versions of the GNU C
compiler fix the header files automatically when installed.
File: autoconf.info, Node: C++ Compiler, Next: Objective C Compiler, Prev: C Compiler, Up: Compilers and Preprocessors
5.10.4 C++ Compiler Characteristics
-----------------------------------
-- Macro: AC_PROG_CXX ([COMPILER-SEARCH-LIST])
Determine a C++ compiler to use. Check whether the environment
variable `CXX' or `CCC' (in that order) is set; if so, then set
output variable `CXX' to its value.
Otherwise, if the macro is invoked without an argument, then
search for a C++ compiler under the likely names (first `g++' and
`c++' then other names). If none of those checks succeed, then as
a last resort set `CXX' to `g++'.
This macro may, however, be invoked with an optional first argument
which, if specified, must be a blank-separated list of C++
compilers to search for. This just gives the user an opportunity
to specify an alternative search list for the C++ compiler. For
example, if you didn't like the default order, then you could
invoke `AC_PROG_CXX' like this:
AC_PROG_CXX([gcc cl KCC CC cxx cc++ xlC aCC c++ g++])
If using the GNU C++ compiler, set shell variable `GXX' to `yes'.
If output variable `CXXFLAGS' was not already set, set it to `-g
-O2' for the GNU C++ compiler (`-O2' on systems where G++ does not
accept `-g'), or `-g' for other compilers. If your package does
not like this default, then it is acceptable to insert the line `:
${CXXFLAGS=""}' after `AC_INIT' and before `AC_PROG_CXX' to select
an empty default instead.
-- Macro: AC_PROG_CXXCPP
Set output variable `CXXCPP' to a command that runs the C++
preprocessor. If `$CXX -E' doesn't work, `/lib/cpp' is used. It
is portable to run `CXXCPP' only on files with a `.c', `.C',
`.cc', or `.cpp' extension.
Some preprocessors don't indicate missing include files by the
error status. For such preprocessors an internal variable is set
that causes other macros to check the standard error from the
preprocessor and consider the test failed if any warnings have
been reported. However, it is not known whether such broken
preprocessors exist for C++.
-- Macro: AC_PROG_CXX_C_O
Test whether the C++ compiler accepts the options `-c' and `-o'
simultaneously, and define `CXX_NO_MINUS_C_MINUS_O', if it does
not.
File: autoconf.info, Node: Objective C Compiler, Next: Objective C++ Compiler, Prev: C++ Compiler, Up: Compilers and Preprocessors
5.10.5 Objective C Compiler Characteristics
-------------------------------------------
-- Macro: AC_PROG_OBJC ([COMPILER-SEARCH-LIST])
Determine an Objective C compiler to use. If `OBJC' is not already
set in the environment, check for Objective C compilers. Set
output variable `OBJC' to the name of the compiler found.
This macro may, however, be invoked with an optional first argument
which, if specified, must be a blank-separated list of Objective C
compilers to search for. This just gives the user an opportunity
to specify an alternative search list for the Objective C
compiler. For example, if you didn't like the default order, then
you could invoke `AC_PROG_OBJC' like this:
AC_PROG_OBJC([gcc objcc objc])
If using the GNU Objective C compiler, set shell variable `GOBJC'
to `yes'. If output variable `OBJCFLAGS' was not already set, set
it to `-g -O2' for the GNU Objective C compiler (`-O2' on systems
where `gcc' does not accept `-g'), or `-g' for other compilers.
-- Macro: AC_PROG_OBJCPP
Set output variable `OBJCPP' to a command that runs the Objective C
preprocessor. If `$OBJC -E' doesn't work, `/lib/cpp' is used.
File: autoconf.info, Node: Objective C++ Compiler, Next: Erlang Compiler and Interpreter, Prev: Objective C Compiler, Up: Compilers and Preprocessors
5.10.6 Objective C++ Compiler Characteristics
---------------------------------------------
-- Macro: AC_PROG_OBJCXX ([COMPILER-SEARCH-LIST])
Determine an Objective C++ compiler to use. If `OBJCXX' is not
already set in the environment, check for Objective C++ compilers.
Set output variable `OBJCXX' to the name of the compiler found.
This macro may, however, be invoked with an optional first argument
which, if specified, must be a blank-separated list of Objective
C++ compilers to search for. This just gives the user an
opportunity to specify an alternative search list for the
Objective C++ compiler. For example, if you didn't like the
default order, then you could invoke `AC_PROG_OBJCXX' like this:
AC_PROG_OBJCXX([gcc g++ objcc++ objcxx])
If using the GNU Objective C++ compiler, set shell variable
`GOBJCXX' to `yes'. If output variable `OBJCXXFLAGS' was not
already set, set it to `-g -O2' for the GNU Objective C++ compiler
(`-O2' on systems where `gcc' does not accept `-g'), or `-g' for
other compilers.
-- Macro: AC_PROG_OBJCXXCPP
Set output variable `OBJCXXCPP' to a command that runs the
Objective C++ preprocessor. If `$OBJCXX -E' doesn't work,
`/lib/cpp' is used.
File: autoconf.info, Node: Erlang Compiler and Interpreter, Next: Fortran Compiler, Prev: Objective C++ Compiler, Up: Compilers and Preprocessors
5.10.7 Erlang Compiler and Interpreter Characteristics
------------------------------------------------------
Autoconf defines the following macros for determining paths to the
essential Erlang/OTP programs:
-- Macro: AC_ERLANG_PATH_ERLC ([VALUE-IF-NOT-FOUND], [PATH = `$PATH'])
Determine an Erlang compiler to use. If `ERLC' is not already set
in the environment, check for `erlc'. Set output variable `ERLC'
to the complete path of the compiler command found. In addition,
if `ERLCFLAGS' is not set in the environment, set it to an empty
value.
The two optional arguments have the same meaning as the two last
arguments of macro `AC_PATH_PROG' for looking for the `erlc'
program. For example, to look for `erlc' only in the
`/usr/lib/erlang/bin' directory:
AC_ERLANG_PATH_ERLC([not found], [/usr/lib/erlang/bin])
-- Macro: AC_ERLANG_NEED_ERLC ([PATH = `$PATH'])
A simplified variant of the `AC_ERLANG_PATH_ERLC' macro, that
prints an error message and exits the `configure' script if the
`erlc' program is not found.
-- Macro: AC_ERLANG_PATH_ERL ([VALUE-IF-NOT-FOUND], [PATH = `$PATH'])
Determine an Erlang interpreter to use. If `ERL' is not already
set in the environment, check for `erl'. Set output variable
`ERL' to the complete path of the interpreter command found.
The two optional arguments have the same meaning as the two last
arguments of macro `AC_PATH_PROG' for looking for the `erl'
program. For example, to look for `erl' only in the
`/usr/lib/erlang/bin' directory:
AC_ERLANG_PATH_ERL([not found], [/usr/lib/erlang/bin])
-- Macro: AC_ERLANG_NEED_ERL ([PATH = `$PATH'])
A simplified variant of the `AC_ERLANG_PATH_ERL' macro, that
prints an error message and exits the `configure' script if the
`erl' program is not found.
File: autoconf.info, Node: Fortran Compiler, Next: Go Compiler, Prev: Erlang Compiler and Interpreter, Up: Compilers and Preprocessors
5.10.8 Fortran Compiler Characteristics
---------------------------------------
The Autoconf Fortran support is divided into two categories: legacy
Fortran 77 macros (`F77'), and modern Fortran macros (`FC'). The
former are intended for traditional Fortran 77 code, and have output
variables like `F77', `FFLAGS', and `FLIBS'. The latter are for newer
programs that can (or must) compile under the newer Fortran standards,
and have output variables like `FC', `FCFLAGS', and `FCLIBS'.
Except for the macros `AC_FC_SRCEXT', `AC_FC_FREEFORM',
`AC_FC_FIXEDFORM', and `AC_FC_LINE_LENGTH' (see below), the `FC' and
`F77' macros behave almost identically, and so they are documented
together in this section.
-- Macro: AC_PROG_F77 ([COMPILER-SEARCH-LIST])
Determine a Fortran 77 compiler to use. If `F77' is not already
set in the environment, then check for `g77' and `f77', and then
some other names. Set the output variable `F77' to the name of
the compiler found.
This macro may, however, be invoked with an optional first argument
which, if specified, must be a blank-separated list of Fortran 77
compilers to search for. This just gives the user an opportunity
to specify an alternative search list for the Fortran 77 compiler.
For example, if you didn't like the default order, then you could
invoke `AC_PROG_F77' like this:
AC_PROG_F77([fl32 f77 fort77 xlf g77 f90 xlf90])
If using `g77' (the GNU Fortran 77 compiler), then set the shell
variable `G77' to `yes'. If the output variable `FFLAGS' was not
already set in the environment, then set it to `-g -02' for `g77'
(or `-O2' where `g77' does not accept `-g'). Otherwise, set
`FFLAGS' to `-g' for all other Fortran 77 compilers.
The result of the GNU test is cached in the
`ac_cv_f77_compiler_gnu' variable, acceptance of `-g' in the
`ac_cv_prog_f77_g' variable.
-- Macro: AC_PROG_FC ([COMPILER-SEARCH-LIST], [DIALECT])
Determine a Fortran compiler to use. If `FC' is not already set in
the environment, then `dialect' is a hint to indicate what Fortran
dialect to search for; the default is to search for the newest
available dialect. Set the output variable `FC' to the name of
the compiler found.
By default, newer dialects are preferred over older dialects, but
if `dialect' is specified then older dialects are preferred
starting with the specified dialect. `dialect' can currently be
one of Fortran 77, Fortran 90, or Fortran 95. However, this is
only a hint of which compiler _name_ to prefer (e.g., `f90' or
`f95'), and no attempt is made to guarantee that a particular
language standard is actually supported. Thus, it is preferable
that you avoid the `dialect' option, and use AC_PROG_FC only for
code compatible with the latest Fortran standard.
This macro may, alternatively, be invoked with an optional first
argument which, if specified, must be a blank-separated list of
Fortran compilers to search for, just as in `AC_PROG_F77'.
If using `gfortran' or `g77' (the GNU Fortran compilers), then set
the shell variable `GFC' to `yes'. If the output variable
`FCFLAGS' was not already set in the environment, then set it to
`-g -02' for GNU `g77' (or `-O2' where `g77' does not accept
`-g'). Otherwise, set `FCFLAGS' to `-g' for all other Fortran
compilers.
The result of the GNU test is cached in the `ac_cv_fc_compiler_gnu'
variable, acceptance of `-g' in the `ac_cv_prog_fc_g' variable.
-- Macro: AC_PROG_F77_C_O
-- Macro: AC_PROG_FC_C_O
Test whether the Fortran compiler accepts the options `-c' and
`-o' simultaneously, and define `F77_NO_MINUS_C_MINUS_O' or
`FC_NO_MINUS_C_MINUS_O', respectively, if it does not.
The result of the test is cached in the `ac_cv_prog_f77_c_o' or
`ac_cv_prog_fc_c_o' variable, respectively.
The following macros check for Fortran compiler characteristics. To
check for characteristics not listed here, use `AC_COMPILE_IFELSE'
(*note Running the Compiler::) or `AC_RUN_IFELSE' (*note Runtime::),
making sure to first set the current language to Fortran 77 or Fortran
via `AC_LANG([Fortran 77])' or `AC_LANG(Fortran)' (*note Language
Choice::).
-- Macro: AC_F77_LIBRARY_LDFLAGS
-- Macro: AC_FC_LIBRARY_LDFLAGS
Determine the linker flags (e.g., `-L' and `-l') for the "Fortran
intrinsic and runtime libraries" that are required to successfully
link a Fortran program or shared library. The output variable
`FLIBS' or `FCLIBS' is set to these flags (which should be
included after `LIBS' when linking).
This macro is intended to be used in those situations when it is
necessary to mix, e.g., C++ and Fortran source code in a single
program or shared library (*note Mixing Fortran 77 With C and C++:
(automake)Mixing Fortran 77 With C and C++.).
For example, if object files from a C++ and Fortran compiler must
be linked together, then the C++ compiler/linker must be used for
linking (since special C++-ish things need to happen at link time
like calling global constructors, instantiating templates,
enabling exception support, etc.).
However, the Fortran intrinsic and runtime libraries must be
linked in as well, but the C++ compiler/linker doesn't know by
default how to add these Fortran 77 libraries. Hence, this macro
was created to determine these Fortran libraries.
The macros `AC_F77_DUMMY_MAIN' and `AC_FC_DUMMY_MAIN' or
`AC_F77_MAIN' and `AC_FC_MAIN' are probably also necessary to link
C/C++ with Fortran; see below. Further, it is highly recommended
that you use `AC_CONFIG_HEADERS' (*note Configuration Headers::)
because the complex defines that the function wrapper macros create
may not work with C/C++ compiler drivers.
These macros internally compute the flag needed to verbose linking
output and cache it in `ac_cv_prog_f77_v' or `ac_cv_prog_fc_v'
variables, respectively. The computed linker flags are cached in
`ac_cv_f77_libs' or `ac_cv_fc_libs', respectively.
-- Macro: AC_F77_DUMMY_MAIN ([ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND =
`AC_MSG_FAILURE'])
-- Macro: AC_FC_DUMMY_MAIN ([ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND =
`AC_MSG_FAILURE'])
With many compilers, the Fortran libraries detected by
`AC_F77_LIBRARY_LDFLAGS' or `AC_FC_LIBRARY_LDFLAGS' provide their
own `main' entry function that initializes things like Fortran
I/O, and which then calls a user-provided entry function named
(say) `MAIN__' to run the user's program. The `AC_F77_DUMMY_MAIN'
and `AC_FC_DUMMY_MAIN' or `AC_F77_MAIN' and `AC_FC_MAIN' macros
figure out how to deal with this interaction.
When using Fortran for purely numerical functions (no I/O, etc.)
often one prefers to provide one's own `main' and skip the Fortran
library initializations. In this case, however, one may still
need to provide a dummy `MAIN__' routine in order to prevent
linking errors on some systems. `AC_F77_DUMMY_MAIN' or
`AC_FC_DUMMY_MAIN' detects whether any such routine is _required_
for linking, and what its name is; the shell variable
`F77_DUMMY_MAIN' or `FC_DUMMY_MAIN' holds this name, `unknown'
when no solution was found, and `none' when no such dummy main is
needed.
By default, ACTION-IF-FOUND defines `F77_DUMMY_MAIN' or
`FC_DUMMY_MAIN' to the name of this routine (e.g., `MAIN__') _if_
it is required. ACTION-IF-NOT-FOUND defaults to exiting with an
error.
In order to link with Fortran routines, the user's C/C++ program
should then include the following code to define the dummy main if
it is needed:
#ifdef F77_DUMMY_MAIN
# ifdef __cplusplus
extern "C"
# endif
int F77_DUMMY_MAIN () { return 1; }
#endif
(Replace `F77' with `FC' for Fortran instead of Fortran 77.)
Note that this macro is called automatically from `AC_F77_WRAPPERS'
or `AC_FC_WRAPPERS'; there is generally no need to call it
explicitly unless one wants to change the default actions.
The result of this macro is cached in the `ac_cv_f77_dummy_main' or
`ac_cv_fc_dummy_main' variable, respectively.
-- Macro: AC_F77_MAIN
-- Macro: AC_FC_MAIN
As discussed above, many Fortran libraries allow you to provide an
entry point called (say) `MAIN__' instead of the usual `main',
which is then called by a `main' function in the Fortran libraries
that initializes things like Fortran I/O. The `AC_F77_MAIN' and
`AC_FC_MAIN' macros detect whether it is _possible_ to utilize
such an alternate main function, and defines `F77_MAIN' and
`FC_MAIN' to the name of the function. (If no alternate main
function name is found, `F77_MAIN' and `FC_MAIN' are simply
defined to `main'.)
Thus, when calling Fortran routines from C that perform things
like I/O, one should use this macro and declare the "main"
function like so:
#ifdef __cplusplus
extern "C"
#endif
int F77_MAIN (int argc, char *argv[]);
(Again, replace `F77' with `FC' for Fortran instead of Fortran 77.)
The result of this macro is cached in the `ac_cv_f77_main' or
`ac_cv_fc_main' variable, respectively.
-- Macro: AC_F77_WRAPPERS
-- Macro: AC_FC_WRAPPERS
Defines C macros `F77_FUNC (name, NAME)', `FC_FUNC (name, NAME)',
`F77_FUNC_(name, NAME)', and `FC_FUNC_(name, NAME)' to properly
mangle the names of C/C++ identifiers, and identifiers with
underscores, respectively, so that they match the name-mangling
scheme used by the Fortran compiler.
Fortran is case-insensitive, and in order to achieve this the
Fortran compiler converts all identifiers into a canonical case
and format. To call a Fortran subroutine from C or to write a C
function that is callable from Fortran, the C program must
explicitly use identifiers in the format expected by the Fortran
compiler. In order to do this, one simply wraps all C identifiers
in one of the macros provided by `AC_F77_WRAPPERS' or
`AC_FC_WRAPPERS'. For example, suppose you have the following
Fortran 77 subroutine:
subroutine foobar (x, y)
double precision x, y
y = 3.14159 * x
return
end
You would then declare its prototype in C or C++ as:
#define FOOBAR_F77 F77_FUNC (foobar, FOOBAR)
#ifdef __cplusplus
extern "C" /* prevent C++ name mangling */
#endif
void FOOBAR_F77 (double *x, double *y);
Note that we pass both the lowercase and uppercase versions of the
function name to `F77_FUNC' so that it can select the right one.
Note also that all parameters to Fortran 77 routines are passed as
pointers (*note Mixing Fortran 77 With C and C++: (automake)Mixing
Fortran 77 With C and C++.).
(Replace `F77' with `FC' for Fortran instead of Fortran 77.)
Although Autoconf tries to be intelligent about detecting the
name-mangling scheme of the Fortran compiler, there may be Fortran
compilers that it doesn't support yet. In this case, the above
code generates a compile-time error, but some other behavior
(e.g., disabling Fortran-related features) can be induced by
checking whether `F77_FUNC' or `FC_FUNC' is defined.
Now, to call that routine from a C program, we would do something
like:
{
double x = 2.7183, y;
FOOBAR_F77 (&x, &y);
}
If the Fortran identifier contains an underscore (e.g., `foo_bar'),
you should use `F77_FUNC_' or `FC_FUNC_' instead of `F77_FUNC' or
`FC_FUNC' (with the same arguments). This is because some Fortran
compilers mangle names differently if they contain an underscore.
The name mangling scheme is encoded in the `ac_cv_f77_mangling' or
`ac_cv_fc_mangling' cache variable, respectively, and also used for
the `AC_F77_FUNC' and `AC_FC_FUNC' macros described below.
-- Macro: AC_F77_FUNC (NAME, [SHELLVAR])
-- Macro: AC_FC_FUNC (NAME, [SHELLVAR])
Given an identifier NAME, set the shell variable SHELLVAR to hold
the mangled version NAME according to the rules of the Fortran
linker (see also `AC_F77_WRAPPERS' or `AC_FC_WRAPPERS'). SHELLVAR
is optional; if it is not supplied, the shell variable is simply
NAME. The purpose of this macro is to give the caller a way to
access the name-mangling information other than through the C
preprocessor as above, for example, to call Fortran routines from
some language other than C/C++.
-- Macro: AC_FC_SRCEXT (EXT, [ACTION-IF-SUCCESS], [ACTION-IF-FAILURE =
`AC_MSG_FAILURE'])
-- Macro: AC_FC_PP_SRCEXT (EXT, [ACTION-IF-SUCCESS],
[ACTION-IF-FAILURE = `AC_MSG_FAILURE'])
By default, the `FC' macros perform their tests using a `.f'
extension for source-code files. Some compilers, however, only
enable newer language features for appropriately named files,
e.g., Fortran 90 features only for `.f90' files, or preprocessing
only with `.F' files or maybe other upper-case extensions. On the
other hand, some other compilers expect all source files to end in
`.f' and require special flags to support other file name
extensions. The `AC_FC_SRCEXT' and `AC_FC_PP_SRCEXT' macros deal
with these issues.
The `AC_FC_SRCEXT' macro tries to get the `FC' compiler to accept
files ending with the extension `.EXT' (i.e., EXT does _not_
contain the dot). If any special compiler flags are needed for
this, it stores them in the output variable `FCFLAGS_EXT'. This
extension and these flags are then used for all subsequent `FC'
tests (until `AC_FC_SRCEXT' or `AC_FC_PP_SRCEXT' is called another
time).
For example, you would use `AC_FC_SRCEXT(f90)' to employ the
`.f90' extension in future tests, and it would set the
`FCFLAGS_f90' output variable with any extra flags that are needed
to compile such files.
Similarly, the `AC_FC_PP_SRCEXT' macro tries to get the `FC'
compiler to preprocess and compile files with the extension
`.EXT'. When both `fpp' and `cpp' style preprocessing are
provided, the former is preferred, as the latter may treat
continuation lines, `//' tokens, and white space differently from
what some Fortran dialects expect. Conversely, if you do not want
files to be preprocessed, use only lower-case characters in the
file name extension. Like with `AC_FC_SRCEXT(f90)', any needed
flags are stored in the `FCFLAGS_EXT' variable.
The `FCFLAGS_EXT' flags can _not_ be simply absorbed into
`FCFLAGS', for two reasons based on the limitations of some
compilers. First, only one `FCFLAGS_EXT' can be used at a time,
so files with different extensions must be compiled separately.
Second, `FCFLAGS_EXT' must appear _immediately_ before the
source-code file name when compiling. So, continuing the example
above, you might compile a `foo.f90' file in your makefile with the
command:
foo.o: foo.f90
$(FC) -c $(FCFLAGS) $(FCFLAGS_f90) '$(srcdir)/foo.f90'
If `AC_FC_SRCEXT' or `AC_FC_PP_SRCEXT' succeeds in compiling files
with the EXT extension, it calls ACTION-IF-SUCCESS (defaults to
nothing). If it fails, and cannot find a way to make the `FC'
compiler accept such files, it calls ACTION-IF-FAILURE (defaults
to exiting with an error message).
The `AC_FC_SRCEXT' and `AC_FC_PP_SRCEXT' macros cache their
results in `ac_cv_fc_srcext_EXT' and `ac_cv_fc_pp_srcext_EXT'
variables, respectively.
-- Macro: AC_FC_PP_DEFINE ([ACTION-IF-SUCCESS], [ACTION-IF-FAILURE =
`AC_MSG_FAILURE'])
Find a flag to specify defines for preprocessed Fortran. Not all
Fortran compilers use `-D'. Substitute `FC_DEFINE' with the
result and call ACTION-IF-SUCCESS (defaults to nothing) if
successful, and ACTION-IF-FAILURE (defaults to failing with an
error message) if not.
This macro calls `AC_FC_PP_SRCEXT([F])' in order to learn how to
preprocess a `conftest.F' file, but restores a previously used
Fortran source file extension afterwards again.
The result of this test is cached in the `ac_cv_fc_pp_define'
variable.
-- Macro: AC_FC_FREEFORM ([ACTION-IF-SUCCESS], [ACTION-IF-FAILURE =
`AC_MSG_FAILURE'])
Try to ensure that the Fortran compiler (`$FC') allows free-format
source code (as opposed to the older fixed-format style from
Fortran 77). If necessary, it may add some additional flags to
`FCFLAGS'.
This macro is most important if you are using the default `.f'
extension, since many compilers interpret this extension as
indicating fixed-format source unless an additional flag is
supplied. If you specify a different extension with
`AC_FC_SRCEXT', such as `.f90', then `AC_FC_FREEFORM' ordinarily
succeeds without modifying `FCFLAGS'. For extensions which the
compiler does not know about, the flag set by the `AC_FC_SRCEXT'
macro might let the compiler assume Fortran 77 by default, however.
If `AC_FC_FREEFORM' succeeds in compiling free-form source, it
calls ACTION-IF-SUCCESS (defaults to nothing). If it fails, it
calls ACTION-IF-FAILURE (defaults to exiting with an error
message).
The result of this test, or `none' or `unknown', is cached in the
`ac_cv_fc_freeform' variable.
-- Macro: AC_FC_FIXEDFORM ([ACTION-IF-SUCCESS], [ACTION-IF-FAILURE =
`AC_MSG_FAILURE'])
Try to ensure that the Fortran compiler (`$FC') allows the old
fixed-format source code (as opposed to free-format style). If
necessary, it may add some additional flags to `FCFLAGS'.
This macro is needed for some compilers alias names like `xlf95'
which assume free-form source code by default, and in case you
want to use fixed-form source with an extension like `.f90' which
many compilers interpret as free-form by default. If you specify
a different extension with `AC_FC_SRCEXT', such as `.f', then
`AC_FC_FIXEDFORM' ordinarily succeeds without modifying `FCFLAGS'.
If `AC_FC_FIXEDFORM' succeeds in compiling fixed-form source, it
calls ACTION-IF-SUCCESS (defaults to nothing). If it fails, it
calls ACTION-IF-FAILURE (defaults to exiting with an error
message).
The result of this test, or `none' or `unknown', is cached in the
`ac_cv_fc_fixedform' variable.
-- Macro: AC_FC_LINE_LENGTH ([LENGTH], [ACTION-IF-SUCCESS],
[ACTION-IF-FAILURE = `AC_MSG_FAILURE'])
Try to ensure that the Fortran compiler (`$FC') accepts long source
code lines. The LENGTH argument may be given as 80, 132, or
unlimited, and defaults to 132. Note that line lengths above 254
columns are not portable, and some compilers do not accept more
than 132 columns at least for fixed format source. If necessary,
it may add some additional flags to `FCFLAGS'.
If `AC_FC_LINE_LENGTH' succeeds in compiling fixed-form source, it
calls ACTION-IF-SUCCESS (defaults to nothing). If it fails, it
calls ACTION-IF-FAILURE (defaults to exiting with an error
message).
The result of this test, or `none' or `unknown', is cached in the
`ac_cv_fc_line_length' variable.
-- Macro: AC_FC_CHECK_BOUNDS ([ACTION-IF-SUCCESS], [ACTION-IF-FAILURE
= `AC_MSG_FAILURE'])
The `AC_FC_CHECK_BOUNDS' macro tries to enable array bounds
checking in the Fortran compiler. If successful, the
ACTION-IF-SUCCESS is called and any needed flags are added to
`FCFLAGS'. Otherwise, ACTION-IF-FAILURE is called, which defaults
to failing with an error message. The macro currently requires
Fortran 90 or a newer dialect.
The result of the macro is cached in the `ac_cv_fc_check_bounds'
variable.
-- Macro: AC_F77_IMPLICIT_NONE ([ACTION-IF-SUCCESS],
[ACTION-IF-FAILURE = `AC_MSG_FAILURE'])
-- Macro: AC_FC_IMPLICIT_NONE ([ACTION-IF-SUCCESS], [ACTION-IF-FAILURE
= `AC_MSG_FAILURE'])
Try to disallow implicit declarations in the Fortran compiler. If
successful, ACTION-IF-SUCCESS is called and any needed flags are
added to `FFLAGS' or `FCFLAGS', respectively. Otherwise,
ACTION-IF-FAILURE is called, which defaults to failing with an
error message.
The result of these macros are cached in the
`ac_cv_f77_implicit_none' and `ac_cv_fc_implicit_none' variables,
respectively.
-- Macro: AC_FC_MODULE_EXTENSION
Find the Fortran 90 module file name extension. Most Fortran 90
compilers store module information in files separate from the
object files. The module files are usually named after the name
of the module rather than the source file name, with characters
possibly turned to upper case, plus an extension, often `.mod'.
Not all compilers use module files at all, or by default. The Cray
Fortran compiler requires `-e m' in order to store and search
module information in `.mod' files rather than in object files.
Likewise, the Fujitsu Fortran compilers uses the `-Am' option to
indicate how module information is stored.
The `AC_FC_MODULE_EXTENSION' macro computes the module extension
without the leading dot, and stores that in the `FC_MODEXT'
variable. If the compiler does not produce module files, or the
extension cannot be determined, `FC_MODEXT' is empty. Typically,
the result of this macro may be used in cleanup `make' rules as
follows:
clean-modules:
-test -z "$(FC_MODEXT)" || rm -f *.$(FC_MODEXT)
The extension, or `unknown', is cached in the
`ac_cv_fc_module_ext' variable.
-- Macro: AC_FC_MODULE_FLAG ([ACTION-IF-SUCCESS], [ACTION-IF-FAILURE =
`AC_MSG_FAILURE'])
Find the compiler flag to include Fortran 90 module information
from another directory, and store that in the `FC_MODINC' variable.
Call ACTION-IF-SUCCESS (defaults to nothing) if successful, and
set `FC_MODINC' to empty and call ACTION-IF-FAILURE (defaults to
exiting with an error message) if not.
Most Fortran 90 compilers provide a way to specify module
directories. Some have separate flags for the directory to write
module files to, and directories to search them in, whereas others
only allow writing to the current directory or to the first
directory specified in the include path. Further, with some
compilers, the module search path and the preprocessor search path
can only be modified with the same flag. Thus, for portability,
write module files to the current directory only and list that as
first directory in the search path.
There may be no whitespace between `FC_MODINC' and the following
directory name, but `FC_MODINC' may contain trailing white space.
For example, if you use Automake and would like to search `../lib'
for module files, you can use the following:
AM_FCFLAGS = $(FC_MODINC). $(FC_MODINC)../lib
Inside `configure' tests, you can use:
if test -n "$FC_MODINC"; then
FCFLAGS="$FCFLAGS $FC_MODINC. $FC_MODINC../lib"
fi
The flag is cached in the `ac_cv_fc_module_flag' variable. The
substituted value of `FC_MODINC' may refer to the `ac_empty' dummy
placeholder empty variable, to avoid losing the significant
trailing whitespace in a `Makefile'.
-- Macro: AC_FC_MODULE_OUTPUT_FLAG ([ACTION-IF-SUCCESS],
[ACTION-IF-FAILURE = `AC_MSG_FAILURE'])
Find the compiler flag to write Fortran 90 module information to
another directory, and store that in the `FC_MODOUT' variable.
Call ACTION-IF-SUCCESS (defaults to nothing) if successful, and
set `FC_MODOUT' to empty and call ACTION-IF-FAILURE (defaults to
exiting with an error message) if not.
Not all Fortran 90 compilers write module files, and of those that
do, not all allow writing to a directory other than the current
one, nor do all have separate flags for writing and reading; see
the description of `AC_FC_MODULE_FLAG' above. If you need to be
able to write to another directory, for maximum portability use
`FC_MODOUT' before any `FC_MODINC' and include both the current
directory and the one you write to in the search path:
AM_FCFLAGS = $(FC_MODOUT)../mod $(FC_MODINC)../mod $(FC_MODINC). ...
The flag is cached in the `ac_cv_fc_module_output_flag' variable.
The substituted value of `FC_MODOUT' may refer to the `ac_empty'
dummy placeholder empty variable, to avoid losing the significant
trailing whitespace in a `Makefile'.
File: autoconf.info, Node: Go Compiler, Prev: Fortran Compiler, Up: Compilers and Preprocessors
5.10.9 Go Compiler Characteristics
----------------------------------
Autoconf provides basic support for the Go programming language when
using the `gccgo' compiler (there is currently no support for the `6g'
and `8g' compilers).
-- Macro: AC_PROG_GO ([COMPILER-SEARCH-LIST])
Find the Go compiler to use. Check whether the environment
variable `GOC' is set; if so, then set output variable `GOC' to its
value.
Otherwise, if the macro is invoked without an argument, then
search for a Go compiler named `gccgo'. If it is not found, then
as a last resort set `GOC' to `gccgo'.
This macro may be invoked with an optional first argument which, if
specified, must be a blank-separated list of Go compilers to
search for.
If output variable `GOFLAGS' was not already set, set it to `-g
-O2'. If your package does not like this default, `GOFLAGS' may
be set before `AC_PROG_GO'.
File: autoconf.info, Node: System Services, Next: Posix Variants, Prev: Compilers and Preprocessors, Up: Existing Tests
5.11 System Services
====================
The following macros check for operating system services or
capabilities.
-- Macro: AC_PATH_X
Try to locate the X Window System include files and libraries. If
the user gave the command line options `--x-includes=DIR' and
`--x-libraries=DIR', use those directories.
If either or both were not given, get the missing values by running
`xmkmf' (or an executable pointed to by the `XMKMF' environment
variable) on a trivial `Imakefile' and examining the makefile that
it produces. Setting `XMKMF' to `false' disables this method.
If this method fails to find the X Window System, `configure'
looks for the files in several directories where they often reside.
If either method is successful, set the shell variables
`x_includes' and `x_libraries' to their locations, unless they are
in directories the compiler searches by default.
If both methods fail, or the user gave the command line option
`--without-x', set the shell variable `no_x' to `yes'; otherwise
set it to the empty string.
-- Macro: AC_PATH_XTRA
An enhanced version of `AC_PATH_X'. It adds the C compiler flags
that X needs to output variable `X_CFLAGS', and the X linker flags
to `X_LIBS'. Define `X_DISPLAY_MISSING' if X is not available.
This macro also checks for special libraries that some systems
need in order to compile X programs. It adds any that the system
needs to output variable `X_EXTRA_LIBS'. And it checks for
special X11R6 libraries that need to be linked with before
`-lX11', and adds any found to the output variable `X_PRE_LIBS'.
-- Macro: AC_SYS_INTERPRETER
Check whether the system supports starting scripts with a line of
the form `#!/bin/sh' to select the interpreter to use for the
script. After running this macro, shell code in `configure.ac'
can check the shell variable `interpval'; it is set to `yes' if
the system supports `#!', `no' if not.
-- Macro: AC_SYS_LARGEFILE
Arrange for 64-bit file offsets, known as large-file support
(http://www.unix-systems.org/version2/whatsnew/lfs20mar.html). On
some hosts, one must use special compiler options to build
programs that can access large files. Append any such options to
the output variable `CC'. Define `_FILE_OFFSET_BITS' and
`_LARGE_FILES' if necessary.
Large-file support can be disabled by configuring with the
`--disable-largefile' option.
If you use this macro, check that your program works even when
`off_t' is wider than `long int', since this is common when
large-file support is enabled. For example, it is not correct to
print an arbitrary `off_t' value `X' with `printf ("%ld", (long
int) X)'.
The LFS introduced the `fseeko' and `ftello' functions to replace
their C counterparts `fseek' and `ftell' that do not use `off_t'.
Take care to use `AC_FUNC_FSEEKO' to make their prototypes
available when using them and large-file support is enabled.
-- Macro: AC_SYS_LONG_FILE_NAMES
If the system supports file names longer than 14 characters, define
`HAVE_LONG_FILE_NAMES'.
-- Macro: AC_SYS_POSIX_TERMIOS
Check to see if the Posix termios headers and functions are
available on the system. If so, set the shell variable
`ac_cv_sys_posix_termios' to `yes'. If not, set the variable to
`no'.
File: autoconf.info, Node: Posix Variants, Next: Erlang Libraries, Prev: System Services, Up: Existing Tests
5.12 Posix Variants
===================
The following macro makes it possible to use features of Posix that are
extensions to C, as well as platform extensions not defined by Posix.
-- Macro: AC_USE_SYSTEM_EXTENSIONS
This macro was introduced in Autoconf 2.60. If possible, enable
extensions to C or Posix on hosts that normally disable the
extensions, typically due to standards-conformance namespace
issues. This should be called before any macros that run the C
compiler. The following preprocessor macros are defined where
appropriate:
`_GNU_SOURCE'
Enable extensions on GNU/Linux.
`__EXTENSIONS__'
Enable general extensions on Solaris.
`_POSIX_PTHREAD_SEMANTICS'
Enable threading extensions on Solaris.
`_TANDEM_SOURCE'
Enable extensions for the HP NonStop platform.
`_ALL_SOURCE'
Enable extensions for AIX 3, and for Interix.
`_POSIX_SOURCE'
Enable Posix functions for Minix.
`_POSIX_1_SOURCE'
Enable additional Posix functions for Minix.
`_MINIX'
Identify Minix platform. This particular preprocessor macro
is obsolescent, and may be removed in a future release of
Autoconf.
File: autoconf.info, Node: Erlang Libraries, Prev: Posix Variants, Up: Existing Tests
5.13 Erlang Libraries
=====================
The following macros check for an installation of Erlang/OTP, and for
the presence of certain Erlang libraries. All those macros require the
configuration of an Erlang interpreter and an Erlang compiler (*note
Erlang Compiler and Interpreter::).
-- Macro: AC_ERLANG_SUBST_ERTS_VER
Set the output variable `ERLANG_ERTS_VER' to the version of the
Erlang runtime system (as returned by Erlang's
`erlang:system_info(version)' function). The result of this test
is cached if caching is enabled when running `configure'. The
`ERLANG_ERTS_VER' variable is not intended to be used for testing
for features of specific ERTS versions, but to be used for
substituting the ERTS version in Erlang/OTP release resource files
(`.rel' files), as shown below.
-- Macro: AC_ERLANG_SUBST_ROOT_DIR
Set the output variable `ERLANG_ROOT_DIR' to the path to the base
directory in which Erlang/OTP is installed (as returned by Erlang's
`code:root_dir/0' function). The result of this test is cached if
caching is enabled when running `configure'.
-- Macro: AC_ERLANG_SUBST_LIB_DIR
Set the output variable `ERLANG_LIB_DIR' to the path of the library
directory of Erlang/OTP (as returned by Erlang's `code:lib_dir/0'
function), which subdirectories each contain an installed
Erlang/OTP library. The result of this test is cached if caching
is enabled when running `configure'.
-- Macro: AC_ERLANG_CHECK_LIB (LIBRARY, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
Test whether the Erlang/OTP library LIBRARY is installed by
calling Erlang's `code:lib_dir/1' function. The result of this
test is cached if caching is enabled when running `configure'.
ACTION-IF-FOUND is a list of shell commands to run if the library
is installed; ACTION-IF-NOT-FOUND is a list of shell commands to
run if it is not. Additionally, if the library is installed, the
output variable `ERLANG_LIB_DIR_LIBRARY' is set to the path to the
library installation directory, and the output variable
`ERLANG_LIB_VER_LIBRARY' is set to the version number that is part
of the subdirectory name, if it is in the standard form
(`LIBRARY-VERSION'). If the directory name does not have a
version part, `ERLANG_LIB_VER_LIBRARY' is set to the empty string.
If the library is not installed, `ERLANG_LIB_DIR_LIBRARY' and
`ERLANG_LIB_VER_LIBRARY' are set to `"not found"'. For example,
to check if library `stdlib' is installed:
AC_ERLANG_CHECK_LIB([stdlib],
[echo "stdlib version \"$ERLANG_LIB_VER_stdlib\""
echo "is installed in \"$ERLANG_LIB_DIR_stdlib\""],
[AC_MSG_ERROR([stdlib was not found!])])
The `ERLANG_LIB_VER_LIBRARY' variables (set by
`AC_ERLANG_CHECK_LIB') and the `ERLANG_ERTS_VER' variable (set by
`AC_ERLANG_SUBST_ERTS_VER') are not intended to be used for
testing for features of specific versions of libraries or of the
Erlang runtime system. Those variables are intended to be
substituted in Erlang release resource files (`.rel' files). For
instance, to generate a `example.rel' file for an application
depending on the `stdlib' library, `configure.ac' could contain:
AC_ERLANG_SUBST_ERTS_VER
AC_ERLANG_CHECK_LIB([stdlib],
[],
[AC_MSG_ERROR([stdlib was not found!])])
AC_CONFIG_FILES([example.rel])
The `example.rel.in' file used to generate `example.rel' should
contain:
{release,
{"@PACKAGE@", "@VERSION@"},
{erts, "@ERLANG_ERTS_VER@"},
[{stdlib, "@ERLANG_LIB_VER_stdlib@"},
{@PACKAGE@, "@VERSION@"}]}.
In addition to the above macros, which test installed Erlang
libraries, the following macros determine the paths to the directories
into which newly built Erlang libraries are to be installed:
-- Macro: AC_ERLANG_SUBST_INSTALL_LIB_DIR
Set the `ERLANG_INSTALL_LIB_DIR' output variable to the directory
into which every built Erlang library should be installed in a
separate subdirectory. If this variable is not set in the
environment when `configure' runs, its default value is
`${libdir}/erlang/lib'.
-- Macro: AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR (LIBRARY, VERSION)
Set the `ERLANG_INSTALL_LIB_DIR_LIBRARY' output variable to the
directory into which the built Erlang library LIBRARY version
VERSION should be installed. If this variable is not set in the
environment when `configure' runs, its default value is
`$ERLANG_INSTALL_LIB_DIR/LIBRARY-VERSION', the value of the
`ERLANG_INSTALL_LIB_DIR' variable being set by the
`AC_ERLANG_SUBST_INSTALL_LIB_DIR' macro.
File: autoconf.info, Node: Writing Tests, Next: Results, Prev: Existing Tests, Up: Top
6 Writing Tests
***************
If the existing feature tests don't do something you need, you have to
write new ones. These macros are the building blocks. They provide
ways for other macros to check whether various kinds of features are
available and report the results.
This chapter contains some suggestions and some of the reasons why
the existing tests are written the way they are. You can also learn a
lot about how to write Autoconf tests by looking at the existing ones.
If something goes wrong in one or more of the Autoconf tests, this
information can help you understand the assumptions behind them, which
might help you figure out how to best solve the problem.
These macros check the output of the compiler system of the current
language (*note Language Choice::). They do not cache the results of
their tests for future use (*note Caching Results::), because they don't
know enough about the information they are checking for to generate a
cache variable name. They also do not print any messages, for the same
reason. The checks for particular kinds of features call these macros
and do cache their results and print messages about what they're
checking for.
When you write a feature test that could be applicable to more than
one software package, the best thing to do is encapsulate it in a new
macro. *Note Writing Autoconf Macros::, for how to do that.
* Menu:
* Language Choice:: Selecting which language to use for testing
* Writing Test Programs:: Forging source files for compilers
* Running the Preprocessor:: Detecting preprocessor symbols
* Running the Compiler:: Detecting language or header features
* Running the Linker:: Detecting library features
* Runtime:: Testing for runtime features
* Systemology:: A zoology of operating systems
* Multiple Cases:: Tests for several possible values
File: autoconf.info, Node: Language Choice, Next: Writing Test Programs, Up: Writing Tests
6.1 Language Choice
===================
Autoconf-generated `configure' scripts check for the C compiler and its
features by default. Packages that use other programming languages
(maybe more than one, e.g., C and C++) need to test features of the
compilers for the respective languages. The following macros determine
which programming language is used in the subsequent tests in
`configure.ac'.
-- Macro: AC_LANG (LANGUAGE)
Do compilation tests using the compiler, preprocessor, and file
extensions for the specified LANGUAGE.
Supported languages are:
`C'
Do compilation tests using `CC' and `CPP' and use extension
`.c' for test programs. Use compilation flags: `CPPFLAGS'
with `CPP', and both `CPPFLAGS' and `CFLAGS' with `CC'.
`C++'
Do compilation tests using `CXX' and `CXXCPP' and use
extension `.C' for test programs. Use compilation flags:
`CPPFLAGS' with `CXXCPP', and both `CPPFLAGS' and `CXXFLAGS'
with `CXX'.
`Fortran 77'
Do compilation tests using `F77' and use extension `.f' for
test programs. Use compilation flags: `FFLAGS'.
`Fortran'
Do compilation tests using `FC' and use extension `.f' (or
whatever has been set by `AC_FC_SRCEXT') for test programs.
Use compilation flags: `FCFLAGS'.
`Erlang'
Compile and execute tests using `ERLC' and `ERL' and use
extension `.erl' for test Erlang modules. Use compilation
flags: `ERLCFLAGS'.
`Objective C'
Do compilation tests using `OBJC' and `OBJCPP' and use
extension `.m' for test programs. Use compilation flags:
`CPPFLAGS' with `OBJCPP', and both `CPPFLAGS' and `OBJCFLAGS'
with `OBJC'.
`Objective C++'
Do compilation tests using `OBJCXX' and `OBJCXXCPP' and use
extension `.mm' for test programs. Use compilation flags:
`CPPFLAGS' with `OBJCXXCPP', and both `CPPFLAGS' and
`OBJCXXFLAGS' with `OBJCXX'.
`Go'
Do compilation tests using `GOC' and use extension `.go' for
test programs. Use compilation flags `GOFLAGS'.
-- Macro: AC_LANG_PUSH (LANGUAGE)
Remember the current language (as set by `AC_LANG') on a stack, and
then select the LANGUAGE. Use this macro and `AC_LANG_POP' in
macros that need to temporarily switch to a particular language.
-- Macro: AC_LANG_POP ([LANGUAGE])
Select the language that is saved on the top of the stack, as set
by `AC_LANG_PUSH', and remove it from the stack.
If given, LANGUAGE specifies the language we just _quit_. It is a
good idea to specify it when it's known (which should be the
case...), since Autoconf detects inconsistencies.
AC_LANG_PUSH([Fortran 77])
# Perform some tests on Fortran 77.
# ...
AC_LANG_POP([Fortran 77])
-- Macro: AC_LANG_ASSERT (LANGUAGE)
Check statically that the current language is LANGUAGE. You
should use this in your language specific macros to avoid that
they be called with an inappropriate language.
This macro runs only at `autoconf' time, and incurs no cost at
`configure' time. Sadly enough and because Autoconf is a two
layer language (1), the macros `AC_LANG_PUSH' and `AC_LANG_POP'
cannot be "optimizing", therefore as much as possible you ought to
avoid using them to wrap your code, rather, require from the user
to run the macro with a correct current language, and check it
with `AC_LANG_ASSERT'. And anyway, that may help the user
understand she is running a Fortran macro while expecting a result
about her Fortran 77 compiler...
-- Macro: AC_REQUIRE_CPP
Ensure that whichever preprocessor would currently be used for
tests has been found. Calls `AC_REQUIRE' (*note Prerequisite
Macros::) with an argument of either `AC_PROG_CPP' or
`AC_PROG_CXXCPP', depending on which language is current.
---------- Footnotes ----------
(1) Because M4 is not aware of Sh code, especially conditionals,
some optimizations that look nice statically may produce incorrect
results at runtime.
File: autoconf.info, Node: Writing Test Programs, Next: Running the Preprocessor, Prev: Language Choice, Up: Writing Tests
6.2 Writing Test Programs
=========================
Autoconf tests follow a common scheme: feed some program with some
input, and most of the time, feed a compiler with some source file.
This section is dedicated to these source samples.
* Menu:
* Guidelines:: General rules for writing test programs
* Test Functions:: Avoiding pitfalls in test programs
* Generating Sources:: Source program boilerplate
File: autoconf.info, Node: Guidelines, Next: Test Functions, Up: Writing Test Programs
6.2.1 Guidelines for Test Programs
----------------------------------
The most important rule to follow when writing testing samples is:
_Look for realism._
This motto means that testing samples must be written with the same
strictness as real programs are written. In particular, you should
avoid "shortcuts" and simplifications.
Don't just play with the preprocessor if you want to prepare a
compilation. For instance, using `cpp' to check whether a header is
functional might let your `configure' accept a header which causes some
_compiler_ error. Do not hesitate to check a header with other headers
included before, especially required headers.
Make sure the symbols you use are properly defined, i.e., refrain
from simply declaring a function yourself instead of including the
proper header.
Test programs should not write to standard output. They should exit
with status 0 if the test succeeds, and with status 1 otherwise, so
that success can be distinguished easily from a core dump or other
failure; segmentation violations and other failures produce a nonzero
exit status. Unless you arrange for `exit' to be declared, test
programs should `return', not `exit', from `main', because on many
systems `exit' is not declared by default.
Test programs can use `#if' or `#ifdef' to check the values of
preprocessor macros defined by tests that have already run. For
example, if you call `AC_HEADER_STDBOOL', then later on in
`configure.ac' you can have a test program that includes `stdbool.h'
conditionally:
#ifdef HAVE_STDBOOL_H
# include
#endif
Both `#if HAVE_STDBOOL_H' and `#ifdef HAVE_STDBOOL_H' will work with
any standard C compiler. Some developers prefer `#if' because it is
easier to read, while others prefer `#ifdef' because it avoids
diagnostics with picky compilers like GCC with the `-Wundef' option.
If a test program needs to use or create a data file, give it a name
that starts with `conftest', such as `conftest.data'. The `configure'
script cleans up by running `rm -f -r conftest*' after running test
programs and if the script is interrupted.
File: autoconf.info, Node: Test Functions, Next: Generating Sources, Prev: Guidelines, Up: Writing Test Programs
6.2.2 Test Functions
--------------------
These days it's safe to assume support for function prototypes
(introduced in C89).
Functions that test programs declare should also be conditionalized
for C++, which requires `extern "C"' prototypes. Make sure to not
include any header files containing clashing prototypes.
#ifdef __cplusplus
extern "C"
#endif
void *valloc (size_t);
If a test program calls a function with invalid parameters (just to
see whether it exists), organize the program to ensure that it never
invokes that function. You can do this by calling it in another
function that is never invoked. You can't do it by putting it after a
call to `exit', because GCC version 2 knows that `exit' never returns
and optimizes out any code that follows it in the same block.
If you include any header files, be sure to call the functions
relevant to them with the correct number of arguments, even if they are
just 0, to avoid compilation errors due to prototypes. GCC version 2
has internal prototypes for several functions that it automatically
inlines; for example, `memcpy'. To avoid errors when checking for
them, either pass them the correct number of arguments or redeclare them
with a different return type (such as `char').
File: autoconf.info, Node: Generating Sources, Prev: Test Functions, Up: Writing Test Programs
6.2.3 Generating Sources
------------------------
Autoconf provides a set of macros that can be used to generate test
source files. They are written to be language generic, i.e., they
actually depend on the current language (*note Language Choice::) to
"format" the output properly.
-- Macro: AC_LANG_CONFTEST (SOURCE)
Save the SOURCE text in the current test source file:
`conftest.EXTENSION' where the EXTENSION depends on the current
language. As of Autoconf 2.63b, the source file also contains the
results of all of the `AC_DEFINE' performed so far.
Note that the SOURCE is evaluated exactly once, like regular
Autoconf macro arguments, and therefore (i) you may pass a macro
invocation, (ii) if not, be sure to double quote if needed.
This macro issues a warning during `autoconf' processing if SOURCE
does not include an expansion of the macro
`AC_LANG_DEFINES_PROVIDED' (note that both `AC_LANG_SOURCE' and
`AC_LANG_PROGRAM' call this macro, and thus avoid the warning).
This macro is seldom called directly, but is used under the hood
by more common macros such as `AC_COMPILE_IFELSE' and
`AC_RUN_IFELSE'.
-- Macro: AC_LANG_DEFINES_PROVIDED
This macro is called as a witness that the file
`conftest.EXTENSION' appropriate for the current language is
complete, including all previously determined results from
`AC_DEFINE'. This macro is seldom called directly, but exists if
you have a compelling reason to write a conftest file without using
`AC_LANG_SOURCE', yet still want to avoid a syntax warning from
`AC_LANG_CONFTEST'.
-- Macro: AC_LANG_SOURCE (SOURCE)
Expands into the SOURCE, with the definition of all the
`AC_DEFINE' performed so far. This macro includes an expansion of
`AC_LANG_DEFINES_PROVIDED'.
In many cases, you may find it more convenient to use the wrapper
`AC_LANG_PROGRAM'.
For instance, executing (observe the double quotation!):
AC_INIT([Hello], [1.0], [bug-hello@example.org], [],
[http://www.example.org/])
AC_DEFINE([HELLO_WORLD], ["Hello, World\n"],
[Greetings string.])
AC_LANG([C])
AC_LANG_CONFTEST(
[AC_LANG_SOURCE([[const char hw[] = "Hello, World\n";]])])
gcc -E -dD conftest.c
on a system with `gcc' installed, results in:
...
# 1 "conftest.c"
#define PACKAGE_NAME "Hello"
#define PACKAGE_TARNAME "hello"
#define PACKAGE_VERSION "1.0"
#define PACKAGE_STRING "Hello 1.0"
#define PACKAGE_BUGREPORT "bug-hello@example.org"
#define PACKAGE_URL "http://www.example.org/"
#define HELLO_WORLD "Hello, World\n"
const char hw[] = "Hello, World\n";
When the test language is Fortran, Erlang, or Go, the `AC_DEFINE'
definitions are not automatically translated into constants in the
source code by this macro.
-- Macro: AC_LANG_PROGRAM (PROLOGUE, BODY)
Expands into a source file which consists of the PROLOGUE, and
then BODY as body of the main function (e.g., `main' in C). Since
it uses `AC_LANG_SOURCE', the features of the latter are available.
For instance:
AC_INIT([Hello], [1.0], [bug-hello@example.org], [],
[http://www.example.org/])
AC_DEFINE([HELLO_WORLD], ["Hello, World\n"],
[Greetings string.])
AC_LANG_CONFTEST(
[AC_LANG_PROGRAM([[const char hw[] = "Hello, World\n";]],
[[fputs (hw, stdout);]])])
gcc -E -dD conftest.c
on a system with `gcc' installed, results in:
...
# 1 "conftest.c"
#define PACKAGE_NAME "Hello"
#define PACKAGE_TARNAME "hello"
#define PACKAGE_VERSION "1.0"
#define PACKAGE_STRING "Hello 1.0"
#define PACKAGE_BUGREPORT "bug-hello@example.org"
#define PACKAGE_URL "http://www.example.org/"
#define HELLO_WORLD "Hello, World\n"
const char hw[] = "Hello, World\n";
int
main ()
{
fputs (hw, stdout);
;
return 0;
}
In Erlang tests, the created source file is that of an Erlang module
called `conftest' (`conftest.erl'). This module defines and exports at
least one `start/0' function, which is called to perform the test. The
PROLOGUE is optional code that is inserted between the module header and
the `start/0' function definition. BODY is the body of the `start/0'
function without the final period (*note Runtime::, about constraints
on this function's behavior).
For instance:
AC_INIT([Hello], [1.0], [bug-hello@example.org])
AC_LANG(Erlang)
AC_LANG_CONFTEST(
[AC_LANG_PROGRAM([[-define(HELLO_WORLD, "Hello, world!").]],
[[io:format("~s~n", [?HELLO_WORLD])]])])
cat conftest.erl
results in:
-module(conftest).
-export([start/0]).
-define(HELLO_WORLD, "Hello, world!").
start() ->
io:format("~s~n", [?HELLO_WORLD])
.
-- Macro: AC_LANG_CALL (PROLOGUE, FUNCTION)
Expands into a source file which consists of the PROLOGUE, and
then a call to the FUNCTION as body of the main function (e.g.,
`main' in C). Since it uses `AC_LANG_PROGRAM', the feature of the
latter are available.
This function will probably be replaced in the future by a version
which would enable specifying the arguments. The use of this
macro is not encouraged, as it violates strongly the typing system.
This macro cannot be used for Erlang tests.
-- Macro: AC_LANG_FUNC_LINK_TRY (FUNCTION)
Expands into a source file which uses the FUNCTION in the body of
the main function (e.g., `main' in C). Since it uses
`AC_LANG_PROGRAM', the features of the latter are available.
As `AC_LANG_CALL', this macro is documented only for completeness.
It is considered to be severely broken, and in the future will be
removed in favor of actual function calls (with properly typed
arguments).
This macro cannot be used for Erlang tests.
File: autoconf.info, Node: Running the Preprocessor, Next: Running the Compiler, Prev: Writing Test Programs, Up: Writing Tests
6.3 Running the Preprocessor
============================
Sometimes one might need to run the preprocessor on some source file.
_Usually it is a bad idea_, as you typically need to _compile_ your
project, not merely run the preprocessor on it; therefore you certainly
want to run the compiler, not the preprocessor. Resist the temptation
of following the easiest path.
Nevertheless, if you need to run the preprocessor, then use
`AC_PREPROC_IFELSE'.
The macros described in this section cannot be used for tests in
Erlang, Fortran, or Go, since those languages require no preprocessor.
-- Macro: AC_PREPROC_IFELSE (INPUT, [ACTION-IF-TRUE],
[ACTION-IF-FALSE])
Run the preprocessor of the current language (*note Language
Choice::) on the INPUT, run the shell commands ACTION-IF-TRUE on
success, ACTION-IF-FALSE otherwise. The INPUT can be made by
`AC_LANG_PROGRAM' and friends.
This macro uses `CPPFLAGS', but not `CFLAGS', because `-g', `-O',
etc. are not valid options to many C preprocessors.
It is customary to report unexpected failures with
`AC_MSG_FAILURE'. If needed, ACTION-IF-TRUE can further access
the preprocessed output in the file `conftest.i'.
For instance:
AC_INIT([Hello], [1.0], [bug-hello@example.org])
AC_DEFINE([HELLO_WORLD], ["Hello, World\n"],
[Greetings string.])
AC_PREPROC_IFELSE(
[AC_LANG_PROGRAM([[const char hw[] = "Hello, World\n";]],
[[fputs (hw, stdout);]])],
[AC_MSG_RESULT([OK])],
[AC_MSG_FAILURE([unexpected preprocessor failure])])
results in:
checking for gcc... gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables...
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ISO C89... none needed
checking how to run the C preprocessor... gcc -E
OK
The macro `AC_TRY_CPP' (*note Obsolete Macros::) used to play the
role of `AC_PREPROC_IFELSE', but double quotes its argument, making it
impossible to use it to elaborate sources. You are encouraged to get
rid of your old use of the macro `AC_TRY_CPP' in favor of
`AC_PREPROC_IFELSE', but, in the first place, are you sure you need to
run the _preprocessor_ and not the compiler?
-- Macro: AC_EGREP_HEADER (PATTERN, HEADER-FILE, ACTION-IF-FOUND,
[ACTION-IF-NOT-FOUND])
If the output of running the preprocessor on the system header file
HEADER-FILE matches the extended regular expression PATTERN,
execute shell commands ACTION-IF-FOUND, otherwise execute
ACTION-IF-NOT-FOUND.
-- Macro: AC_EGREP_CPP (PATTERN, PROGRAM, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
PROGRAM is the text of a C or C++ program, on which shell
variable, back quote, and backslash substitutions are performed.
If the output of running the preprocessor on PROGRAM matches the
extended regular expression PATTERN, execute shell commands
ACTION-IF-FOUND, otherwise execute ACTION-IF-NOT-FOUND.
File: autoconf.info, Node: Running the Compiler, Next: Running the Linker, Prev: Running the Preprocessor, Up: Writing Tests
6.4 Running the Compiler
========================
To check for a syntax feature of the current language's (*note Language
Choice::) compiler, such as whether it recognizes a certain keyword, or
simply to try some library feature, use `AC_COMPILE_IFELSE' to try to
compile a small program that uses that feature.
-- Macro: AC_COMPILE_IFELSE (INPUT, [ACTION-IF-TRUE],
[ACTION-IF-FALSE])
Run the compiler and compilation flags of the current language
(*note Language Choice::) on the INPUT, run the shell commands
ACTION-IF-TRUE on success, ACTION-IF-FALSE otherwise. The INPUT
can be made by `AC_LANG_PROGRAM' and friends.
It is customary to report unexpected failures with
`AC_MSG_FAILURE'. This macro does not try to link; use
`AC_LINK_IFELSE' if you need to do that (*note Running the
Linker::). If needed, ACTION-IF-TRUE can further access the
just-compiled object file `conftest.$OBJEXT'.
This macro uses `AC_REQUIRE' for the compiler associated with the
current language, which means that if the compiler has not yet been
determined, the compiler determination will be made prior to the
body of the outermost `AC_DEFUN' macro that triggered this macro to
expand (*note Expanded Before Required::).
For tests in Erlang, the INPUT must be the source code of a module
named `conftest'. `AC_COMPILE_IFELSE' generates a `conftest.beam' file
that can be interpreted by the Erlang virtual machine (`ERL'). It is
recommended to use `AC_LANG_PROGRAM' to specify the test program, to
ensure that the Erlang module has the right name.
File: autoconf.info, Node: Running the Linker, Next: Runtime, Prev: Running the Compiler, Up: Writing Tests
6.5 Running the Linker
======================
To check for a library, a function, or a global variable, Autoconf
`configure' scripts try to compile and link a small program that uses
it. This is unlike Metaconfig, which by default uses `nm' or `ar' on
the C library to try to figure out which functions are available.
Trying to link with the function is usually a more reliable approach
because it avoids dealing with the variations in the options and output
formats of `nm' and `ar' and in the location of the standard libraries.
It also allows configuring for cross-compilation or checking a
function's runtime behavior if needed. On the other hand, it can be
slower than scanning the libraries once, but accuracy is more important
than speed.
`AC_LINK_IFELSE' is used to compile test programs to test for
functions and global variables. It is also used by `AC_CHECK_LIB' to
check for libraries (*note Libraries::), by adding the library being
checked for to `LIBS' temporarily and trying to link a small program.
-- Macro: AC_LINK_IFELSE (INPUT, [ACTION-IF-TRUE], [ACTION-IF-FALSE])
Run the compiler (and compilation flags) and the linker of the
current language (*note Language Choice::) on the INPUT, run the
shell commands ACTION-IF-TRUE on success, ACTION-IF-FALSE
otherwise. The INPUT can be made by `AC_LANG_PROGRAM' and
friends. If needed, ACTION-IF-TRUE can further access the
just-linked program file `conftest$EXEEXT'.
`LDFLAGS' and `LIBS' are used for linking, in addition to the
current compilation flags.
It is customary to report unexpected failures with
`AC_MSG_FAILURE'. This macro does not try to execute the program;
use `AC_RUN_IFELSE' if you need to do that (*note Runtime::).
The `AC_LINK_IFELSE' macro cannot be used for Erlang tests, since
Erlang programs are interpreted and do not require linking.
File: autoconf.info, Node: Runtime, Next: Systemology, Prev: Running the Linker, Up: Writing Tests
6.6 Checking Runtime Behavior
=============================
Sometimes you need to find out how a system performs at runtime, such
as whether a given function has a certain capability or bug. If you
can, make such checks when your program runs instead of when it is
configured. You can check for things like the machine's endianness when
your program initializes itself.
If you really need to test for a runtime behavior while configuring,
you can write a test program to determine the result, and compile and
run it using `AC_RUN_IFELSE'. Avoid running test programs if possible,
because this prevents people from configuring your package for
cross-compiling.
-- Macro: AC_RUN_IFELSE (INPUT, [ACTION-IF-TRUE], [ACTION-IF-FALSE],
[ACTION-IF-CROSS-COMPILING = `AC_MSG_FAILURE'])
Run the compiler (and compilation flags) and the linker of the
current language (*note Language Choice::) on the INPUT, then
execute the resulting program. If the program returns an exit
status of 0 when executed, run shell commands ACTION-IF-TRUE.
Otherwise, run shell commands ACTION-IF-FALSE.
The INPUT can be made by `AC_LANG_PROGRAM' and friends. `LDFLAGS'
and `LIBS' are used for linking, in addition to the compilation
flags of the current language (*note Language Choice::).
Additionally, ACTION-IF-TRUE can run `./conftest$EXEEXT' for
further testing.
In the ACTION-IF-FALSE section, the failing exit status is
available in the shell variable `$?'. This exit status might be
that of a failed compilation, or it might be that of a failed
program execution.
If cross-compilation mode is enabled (this is the case if either
the compiler being used does not produce executables that run on
the system where `configure' is being run, or if the options
`--build' and `--host' were both specified and their values are
different), then the test program is not run. If the optional
shell commands ACTION-IF-CROSS-COMPILING are given, those commands
are run instead; typically these commands provide pessimistic
defaults that allow cross-compilation to work even if the guess
was wrong. If the fourth argument is empty or omitted, but
cross-compilation is detected, then `configure' prints an error
message and exits. If you want your package to be useful in a
cross-compilation scenario, you _should_ provide a non-empty
ACTION-IF-CROSS-COMPILING clause, as well as wrap the
`AC_RUN_IFELSE' compilation inside an `AC_CACHE_CHECK' (*note
Caching Results::) which allows the user to override the
pessimistic default if needed.
It is customary to report unexpected failures with
`AC_MSG_FAILURE'.
`autoconf' prints a warning message when creating `configure' each
time it encounters a call to `AC_RUN_IFELSE' with no
ACTION-IF-CROSS-COMPILING argument given. If you are not concerned
about users configuring your package for cross-compilation, you may
ignore the warning. A few of the macros distributed with Autoconf
produce this warning message; but if this is a problem for you, please
report it as a bug, along with an appropriate pessimistic guess to use
instead.
To configure for cross-compiling you can also choose a value for
those parameters based on the canonical system name (*note Manual
Configuration::). Alternatively, set up a test results cache file with
the correct values for the host system (*note Caching Results::).
To provide a default for calls of `AC_RUN_IFELSE' that are embedded
in other macros, including a few of the ones that come with Autoconf,
you can test whether the shell variable `cross_compiling' is set to
`yes', and then use an alternate method to get the results instead of
calling the macros.
It is also permissible to temporarily assign to `cross_compiling' in
order to force tests to behave as though they are in a
cross-compilation environment, particularly since this provides a way to
test your ACTION-IF-CROSS-COMPILING even when you are not using a
cross-compiler.
# We temporarily set cross-compile mode to force AC_COMPUTE_INT
# to use the slow link-only method
save_cross_compiling=$cross_compiling
cross_compiling=yes
AC_COMPUTE_INT([...])
cross_compiling=$save_cross_compiling
A C or C++ runtime test should be portable. *Note Portable C and
C++::.
Erlang tests must exit themselves the Erlang VM by calling the
`halt/1' function: the given status code is used to determine the
success of the test (status is `0') or its failure (status is different
than `0'), as explained above. It must be noted that data output
through the standard output (e.g., using `io:format/2') may be
truncated when halting the VM. Therefore, if a test must output
configuration information, it is recommended to create and to output
data into the temporary file named `conftest.out', using the functions
of module `file'. The `conftest.out' file is automatically deleted by
the `AC_RUN_IFELSE' macro. For instance, a simplified implementation
of Autoconf's `AC_ERLANG_SUBST_LIB_DIR' macro is:
AC_INIT([LibdirTest], [1.0], [bug-libdirtest@example.org])
AC_ERLANG_NEED_ERL
AC_LANG(Erlang)
AC_RUN_IFELSE(
[AC_LANG_PROGRAM([], [dnl
file:write_file("conftest.out", code:lib_dir()),
halt(0)])],
[echo "code:lib_dir() returned: `cat conftest.out`"],
[AC_MSG_FAILURE([test Erlang program execution failed])])
File: autoconf.info, Node: Systemology, Next: Multiple Cases, Prev: Runtime, Up: Writing Tests
6.7 Systemology
===============
This section aims at presenting some systems and pointers to
documentation. It may help you addressing particular problems reported
by users.
Posix-conforming systems (http://www.opengroup.org/susv3) are
derived from the Unix operating system
(http://www.bell-labs.com/history/unix/).
The Rosetta Stone for Unix (http://bhami.com/rosetta.html) contains
a table correlating the features of various Posix-conforming systems.
Unix History (http://www.levenez.com/unix/) is a simplified diagram of
how many Unix systems were derived from each other.
The Heirloom Project (http://heirloom.sourceforge.net/) provides
some variants of traditional implementations of Unix utilities.
Darwin
Darwin is also known as Mac OS X. Beware that the file system
_can_ be case-preserving, but case insensitive. This can cause
nasty problems, since for instance the installation attempt for a
package having an `INSTALL' file can result in `make install'
report that nothing was to be done!
That's all dependent on whether the file system is a UFS (case
sensitive) or HFS+ (case preserving). By default Apple wants you
to install the OS on HFS+. Unfortunately, there are some pieces of
software which really need to be built on UFS. We may want to
rebuild Darwin to have both UFS and HFS+ available (and put the
/local/build tree on the UFS).
QNX 4.25
QNX is a realtime operating system running on Intel architecture
meant to be scalable from the small embedded systems to the hundred
processor super-computer. It claims to be Posix certified. More
information is available on the QNX home page
(http://www.qnx.com/).
Tru64
Documentation of several versions of Tru64
(http://h30097.www3.hp.com/docs/) is available in different
formats.
Unix version 7
Officially this was called the "Seventh Edition" of "the UNIX
time-sharing system" but we use the more-common name "Unix version
7". Documentation is available in the Unix Seventh Edition Manual
(http://plan9.bell-labs.com/7thEdMan/). Previous versions of Unix
are called "Unix version 6", etc., but they were not as widely
used.
File: autoconf.info, Node: Multiple Cases, Prev: Systemology, Up: Writing Tests
6.8 Multiple Cases
==================
Some operations are accomplished in several possible ways, depending on
the OS variant. Checking for them essentially requires a "case
statement". Autoconf does not directly provide one; however, it is
easy to simulate by using a shell variable to keep track of whether a
way to perform the operation has been found yet.
Here is an example that uses the shell variable `fstype' to keep
track of whether the remaining cases need to be checked. Note that
since the value of `fstype' is under our control, we don't have to use
the longer `test "x$fstype" = xno'.
AC_MSG_CHECKING([how to get file system type])
fstype=no
# The order of these tests is important.
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include
#include ]])],
[AC_DEFINE([FSTYPE_STATVFS], [1],
[Define if statvfs exists.])
fstype=SVR4])
if test $fstype = no; then
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include
#include ]])],
[AC_DEFINE([FSTYPE_USG_STATFS], [1],
[Define if USG statfs.])
fstype=SVR3])
fi
if test $fstype = no; then
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include
#include ]])]),
[AC_DEFINE([FSTYPE_AIX_STATFS], [1],
[Define if AIX statfs.])
fstype=AIX])
fi
# (more cases omitted here)
AC_MSG_RESULT([$fstype])
File: autoconf.info, Node: Results, Next: Programming in M4, Prev: Writing Tests, Up: Top
7 Results of Tests
******************
Once `configure' has determined whether a feature exists, what can it
do to record that information? There are four sorts of things it can
do: define a C preprocessor symbol, set a variable in the output files,
save the result in a cache file for future `configure' runs, and print
a message letting the user know the result of the test.
* Menu:
* Defining Symbols:: Defining C preprocessor symbols
* Setting Output Variables:: Replacing variables in output files
* Special Chars in Variables:: Characters to beware of in variables
* Caching Results:: Speeding up subsequent `configure' runs
* Printing Messages:: Notifying `configure' users
File: autoconf.info, Node: Defining Symbols, Next: Setting Output Variables, Up: Results
7.1 Defining C Preprocessor Symbols
===================================
A common action to take in response to a feature test is to define a C
preprocessor symbol indicating the results of the test. That is done by
calling `AC_DEFINE' or `AC_DEFINE_UNQUOTED'.
By default, `AC_OUTPUT' places the symbols defined by these macros
into the output variable `DEFS', which contains an option
`-DSYMBOL=VALUE' for each symbol defined. Unlike in Autoconf version
1, there is no variable `DEFS' defined while `configure' is running.
To check whether Autoconf macros have already defined a certain C
preprocessor symbol, test the value of the appropriate cache variable,
as in this example:
AC_CHECK_FUNC([vprintf], [AC_DEFINE([HAVE_VPRINTF], [1],
[Define if vprintf exists.])])
if test "x$ac_cv_func_vprintf" != xyes; then
AC_CHECK_FUNC([_doprnt], [AC_DEFINE([HAVE_DOPRNT], [1],
[Define if _doprnt exists.])])
fi
If `AC_CONFIG_HEADERS' has been called, then instead of creating
`DEFS', `AC_OUTPUT' creates a header file by substituting the correct
values into `#define' statements in a template file. *Note
Configuration Headers::, for more information about this kind of output.
-- Macro: AC_DEFINE (VARIABLE, VALUE, [DESCRIPTION])
-- Macro: AC_DEFINE (VARIABLE)
Define VARIABLE to VALUE (verbatim), by defining a C preprocessor
macro for VARIABLE. VARIABLE should be a C identifier, optionally
suffixed by a parenthesized argument list to define a C
preprocessor macro with arguments. The macro argument list, if
present, should be a comma-separated list of C identifiers,
possibly terminated by an ellipsis `...' if C99 syntax is employed.
VARIABLE should not contain comments, white space, trigraphs,
backslash-newlines, universal character names, or non-ASCII
characters.
VALUE may contain backslash-escaped newlines, which will be
preserved if you use `AC_CONFIG_HEADERS' but flattened if passed
via `@DEFS@' (with no effect on the compilation, since the
preprocessor sees only one line in the first place). VALUE should
not contain raw newlines. If you are not using
`AC_CONFIG_HEADERS', VALUE should not contain any `#' characters,
as `make' tends to eat them. To use a shell variable, use
`AC_DEFINE_UNQUOTED' instead.
DESCRIPTION is only useful if you are using `AC_CONFIG_HEADERS'.
In this case, DESCRIPTION is put into the generated `config.h.in'
as the comment before the macro define. The following example
defines the C preprocessor variable `EQUATION' to be the string
constant `"$a > $b"':
AC_DEFINE([EQUATION], ["$a > $b"],
[Equation string.])
If neither VALUE nor DESCRIPTION are given, then VALUE defaults to
1 instead of to the empty string. This is for backwards
compatibility with older versions of Autoconf, but this usage is
obsolescent and may be withdrawn in future versions of Autoconf.
If the VARIABLE is a literal string, it is passed to
`m4_pattern_allow' (*note Forbidden Patterns::).
If multiple `AC_DEFINE' statements are executed for the same
VARIABLE name (not counting any parenthesized argument list), the
last one wins.
-- Macro: AC_DEFINE_UNQUOTED (VARIABLE, VALUE, [DESCRIPTION])
-- Macro: AC_DEFINE_UNQUOTED (VARIABLE)
Like `AC_DEFINE', but three shell expansions are
performed--once--on VARIABLE and VALUE: variable expansion (`$'),
command substitution (``'), and backslash escaping (`\'), as if in
an unquoted here-document. Single and double quote characters in
the value have no special meaning. Use this macro instead of
`AC_DEFINE' when VARIABLE or VALUE is a shell variable. Examples:
AC_DEFINE_UNQUOTED([config_machfile], ["$machfile"],
[Configuration machine file.])
AC_DEFINE_UNQUOTED([GETGROUPS_T], [$ac_cv_type_getgroups],
[getgroups return type.])
AC_DEFINE_UNQUOTED([$ac_tr_hdr], [1],
[Translated header name.])
Due to a syntactical bizarreness of the Bourne shell, do not use
semicolons to separate `AC_DEFINE' or `AC_DEFINE_UNQUOTED' calls from
other macro calls or shell code; that can cause syntax errors in the
resulting `configure' script. Use either blanks or newlines. That is,
do this:
AC_CHECK_HEADER([elf.h],
[AC_DEFINE([SVR4], [1], [System V Release 4]) LIBS="-lelf $LIBS"])
or this:
AC_CHECK_HEADER([elf.h],
[AC_DEFINE([SVR4], [1], [System V Release 4])
LIBS="-lelf $LIBS"])
instead of this:
AC_CHECK_HEADER([elf.h],
[AC_DEFINE([SVR4], [1], [System V Release 4]); LIBS="-lelf $LIBS"])
File: autoconf.info, Node: Setting Output Variables, Next: Special Chars in Variables, Prev: Defining Symbols, Up: Results
7.2 Setting Output Variables
============================
Another way to record the results of tests is to set "output
variables", which are shell variables whose values are substituted into
files that `configure' outputs. The two macros below create new output
variables. *Note Preset Output Variables::, for a list of output
variables that are always available.
-- Macro: AC_SUBST (VARIABLE, [VALUE])
Create an output variable from a shell variable. Make `AC_OUTPUT'
substitute the variable VARIABLE into output files (typically one
or more makefiles). This means that `AC_OUTPUT' replaces
instances of `@VARIABLE@' in input files with the value that the
shell variable VARIABLE has when `AC_OUTPUT' is called. The value
can contain any non-`NUL' character, including newline. If you
are using Automake 1.11 or newer, for newlines in values you might
want to consider using `AM_SUBST_NOTMAKE' to prevent `automake'
from adding a line `VARIABLE = @VARIABLE@' to the `Makefile.in'
files (*note Automake: (automake)Optional.).
Variable occurrences should not overlap: e.g., an input file should
not contain `@VAR1@VAR2@' if VAR1 and VAR2 are variable names.
The substituted value is not rescanned for more output variables;
occurrences of `@VARIABLE@' in the value are inserted literally
into the output file. (The algorithm uses the special marker
`|#_!!_#|' internally, so neither the substituted value nor the
output file may contain `|#_!!_#|'.)
If VALUE is given, in addition assign it to VARIABLE.
The string VARIABLE is passed to `m4_pattern_allow' (*note
Forbidden Patterns::).
-- Macro: AC_SUBST_FILE (VARIABLE)
Another way to create an output variable from a shell variable.
Make `AC_OUTPUT' insert (without substitutions) the contents of
the file named by shell variable VARIABLE into output files. This
means that `AC_OUTPUT' replaces instances of `@VARIABLE@' in
output files (such as `Makefile.in') with the contents of the file
that the shell variable VARIABLE names when `AC_OUTPUT' is called.
Set the variable to `/dev/null' for cases that do not have a file
to insert. This substitution occurs only when the `@VARIABLE@' is
on a line by itself, optionally surrounded by spaces and tabs. The
substitution replaces the whole line, including the spaces, tabs,
and the terminating newline.
This macro is useful for inserting makefile fragments containing
special dependencies or other `make' directives for particular host
or target types into makefiles. For example, `configure.ac' could
contain:
AC_SUBST_FILE([host_frag])
host_frag=$srcdir/conf/sun4.mh
and then a `Makefile.in' could contain:
@host_frag@
The string VARIABLE is passed to `m4_pattern_allow' (*note
Forbidden Patterns::).
Running `configure' in varying environments can be extremely
dangerous. If for instance the user runs `CC=bizarre-cc ./configure',
then the cache, `config.h', and many other output files depend upon
`bizarre-cc' being the C compiler. If for some reason the user runs
`./configure' again, or if it is run via `./config.status --recheck',
(*Note Automatic Remaking::, and *note config.status Invocation::),
then the configuration can be inconsistent, composed of results
depending upon two different compilers.
Environment variables that affect this situation, such as `CC'
above, are called "precious variables", and can be declared as such by
`AC_ARG_VAR'.
-- Macro: AC_ARG_VAR (VARIABLE, DESCRIPTION)
Declare VARIABLE is a precious variable, and include its
DESCRIPTION in the variable section of `./configure --help'.
Being precious means that
- VARIABLE is substituted via `AC_SUBST'.
- The value of VARIABLE when `configure' was launched is saved
in the cache, including if it was not specified on the command
line but via the environment. Indeed, while `configure' can
notice the definition of `CC' in `./configure CC=bizarre-cc',
it is impossible to notice it in `CC=bizarre-cc ./configure',
which, unfortunately, is what most users do.
We emphasize that it is the _initial_ value of VARIABLE which
is saved, not that found during the execution of `configure'.
Indeed, specifying `./configure FOO=foo' and letting
`./configure' guess that `FOO' is `foo' can be two different
things.
- VARIABLE is checked for consistency between two `configure'
runs. For instance:
$ ./configure --silent --config-cache
$ CC=cc ./configure --silent --config-cache
configure: error: `CC' was not set in the previous run
configure: error: changes in the environment can compromise \
the build
configure: error: run `make distclean' and/or \
`rm config.cache' and start over
and similarly if the variable is unset, or if its content is
changed. If the content has white space changes only, then
the error is degraded to a warning only, but the old value is
reused.
- VARIABLE is kept during automatic reconfiguration (*note
config.status Invocation::) as if it had been passed as a
command line argument, including when no cache is used:
$ CC=/usr/bin/cc ./configure var=raboof --silent
$ ./config.status --recheck
running CONFIG_SHELL=/bin/sh /bin/sh ./configure var=raboof \
CC=/usr/bin/cc --no-create --no-recursion
File: autoconf.info, Node: Special Chars in Variables, Next: Caching Results, Prev: Setting Output Variables, Up: Results
7.3 Special Characters in Output Variables
==========================================
Many output variables are intended to be evaluated both by `make' and
by the shell. Some characters are expanded differently in these two
contexts, so to avoid confusion these variables' values should not
contain any of the following characters:
" # $ & ' ( ) * ; < > ? [ \ ^ ` |
Also, these variables' values should neither contain newlines, nor
start with `~', nor contain white space or `:' immediately followed by
`~'. The values can contain nonempty sequences of white space
characters like tabs and spaces, but each such sequence might
arbitrarily be replaced by a single space during substitution.
These restrictions apply both to the values that `configure'
computes, and to the values set directly by the user. For example, the
following invocations of `configure' are problematic, since they
attempt to use special characters within `CPPFLAGS' and white space
within `$(srcdir)':
CPPFLAGS='-DOUCH="&\"#$*?"' '../My Source/ouch-1.0/configure'
'../My Source/ouch-1.0/configure' CPPFLAGS='-DOUCH="&\"#$*?"'
File: autoconf.info, Node: Caching Results, Next: Printing Messages, Prev: Special Chars in Variables, Up: Results
7.4 Caching Results
===================
To avoid checking for the same features repeatedly in various
`configure' scripts (or in repeated runs of one script), `configure'
can optionally save the results of many checks in a "cache file" (*note
Cache Files::). If a `configure' script runs with caching enabled and
finds a cache file, it reads the results of previous runs from the
cache and avoids rerunning those checks. As a result, `configure' can
then run much faster than if it had to perform all of the checks every
time.
-- Macro: AC_CACHE_VAL (CACHE-ID, COMMANDS-TO-SET-IT)
Ensure that the results of the check identified by CACHE-ID are
available. If the results of the check were in the cache file
that was read, and `configure' was not given the `--quiet' or
`--silent' option, print a message saying that the result was
cached; otherwise, run the shell commands COMMANDS-TO-SET-IT. If
the shell commands are run to determine the value, the value is
saved in the cache file just before `configure' creates its output
files. *Note Cache Variable Names::, for how to choose the name
of the CACHE-ID variable.
The COMMANDS-TO-SET-IT _must have no side effects_ except for
setting the variable CACHE-ID, see below.
-- Macro: AC_CACHE_CHECK (MESSAGE, CACHE-ID, COMMANDS-TO-SET-IT)
A wrapper for `AC_CACHE_VAL' that takes care of printing the
messages. This macro provides a convenient shorthand for the most
common way to use these macros. It calls `AC_MSG_CHECKING' for
MESSAGE, then `AC_CACHE_VAL' with the CACHE-ID and COMMANDS
arguments, and `AC_MSG_RESULT' with CACHE-ID.
The COMMANDS-TO-SET-IT _must have no side effects_ except for
setting the variable CACHE-ID, see below.
It is common to find buggy macros using `AC_CACHE_VAL' or
`AC_CACHE_CHECK', because people are tempted to call `AC_DEFINE' in the
COMMANDS-TO-SET-IT. Instead, the code that _follows_ the call to
`AC_CACHE_VAL' should call `AC_DEFINE', by examining the value of the
cache variable. For instance, the following macro is broken:
AC_DEFUN([AC_SHELL_TRUE],
[AC_CACHE_CHECK([whether true(1) works], [my_cv_shell_true_works],
[my_cv_shell_true_works=no
(true) 2>/dev/null && my_cv_shell_true_works=yes
if test "x$my_cv_shell_true_works" = xyes; then
AC_DEFINE([TRUE_WORKS], [1],
[Define if `true(1)' works properly.])
fi])
])
This fails if the cache is enabled: the second time this macro is run,
`TRUE_WORKS' _will not be defined_. The proper implementation is:
AC_DEFUN([AC_SHELL_TRUE],
[AC_CACHE_CHECK([whether true(1) works], [my_cv_shell_true_works],
[my_cv_shell_true_works=no
(true) 2>/dev/null && my_cv_shell_true_works=yes])
if test "x$my_cv_shell_true_works" = xyes; then
AC_DEFINE([TRUE_WORKS], [1],
[Define if `true(1)' works properly.])
fi
])
Also, COMMANDS-TO-SET-IT should not print any messages, for example
with `AC_MSG_CHECKING'; do that before calling `AC_CACHE_VAL', so the
messages are printed regardless of whether the results of the check are
retrieved from the cache or determined by running the shell commands.
* Menu:
* Cache Variable Names:: Shell variables used in caches
* Cache Files:: Files `configure' uses for caching
* Cache Checkpointing:: Loading and saving the cache file
File: autoconf.info, Node: Cache Variable Names, Next: Cache Files, Up: Caching Results
7.4.1 Cache Variable Names
--------------------------
The names of cache variables should have the following format:
PACKAGE-PREFIX_cv_VALUE-TYPE_SPECIFIC-VALUE_[ADDITIONAL-OPTIONS]
for example, `ac_cv_header_stat_broken' or
`ac_cv_prog_gcc_traditional'. The parts of the variable name are:
PACKAGE-PREFIX
An abbreviation for your package or organization; the same prefix
you begin local Autoconf macros with, except lowercase by
convention. For cache values used by the distributed Autoconf
macros, this value is `ac'.
`_cv_'
Indicates that this shell variable is a cache value. This string
_must_ be present in the variable name, including the leading
underscore.
VALUE-TYPE
A convention for classifying cache values, to produce a rational
naming system. The values used in Autoconf are listed in *note
Macro Names::.
SPECIFIC-VALUE
Which member of the class of cache values this test applies to.
For example, which function (`alloca'), program (`gcc'), or output
variable (`INSTALL').
ADDITIONAL-OPTIONS
Any particular behavior of the specific member that this test
applies to. For example, `broken' or `set'. This part of the
name may be omitted if it does not apply.
The values assigned to cache variables may not contain newlines.
Usually, their values are Boolean (`yes' or `no') or the names of files
or functions; so this is not an important restriction. *note Cache
Variable Index:: for an index of cache variables with documented
semantics.
File: autoconf.info, Node: Cache Files, Next: Cache Checkpointing, Prev: Cache Variable Names, Up: Caching Results
7.4.2 Cache Files
-----------------
A cache file is a shell script that caches the results of configure
tests run on one system so they can be shared between configure scripts
and configure runs. It is not useful on other systems. If its contents
are invalid for some reason, the user may delete or edit it, or override
documented cache variables on the `configure' command line.
By default, `configure' uses no cache file, to avoid problems caused
by accidental use of stale cache files.
To enable caching, `configure' accepts `--config-cache' (or `-C') to
cache results in the file `config.cache'. Alternatively,
`--cache-file=FILE' specifies that FILE be the cache file. The cache
file is created if it does not exist already. When `configure' calls
`configure' scripts in subdirectories, it uses the `--cache-file'
argument so that they share the same cache. *Note Subdirectories::,
for information on configuring subdirectories with the
`AC_CONFIG_SUBDIRS' macro.
`config.status' only pays attention to the cache file if it is given
the `--recheck' option, which makes it rerun `configure'.
It is wrong to try to distribute cache files for particular system
types. There is too much room for error in doing that, and too much
administrative overhead in maintaining them. For any features that
can't be guessed automatically, use the standard method of the canonical
system type and linking files (*note Manual Configuration::).
The site initialization script can specify a site-wide cache file to
use, instead of the usual per-program cache. In this case, the cache
file gradually accumulates information whenever someone runs a new
`configure' script. (Running `configure' merges the new cache results
with the existing cache file.) This may cause problems, however, if
the system configuration (e.g., the installed libraries or compilers)
changes and the stale cache file is not deleted.
If `configure' is interrupted at the right time when it updates a
cache file outside of the build directory where the `configure' script
is run, it may leave behind a temporary file named after the cache file
with digits following it. You may safely delete such a file.
File: autoconf.info, Node: Cache Checkpointing, Prev: Cache Files, Up: Caching Results
7.4.3 Cache Checkpointing
-------------------------
If your configure script, or a macro called from `configure.ac', happens
to abort the configure process, it may be useful to checkpoint the cache
a few times at key points using `AC_CACHE_SAVE'. Doing so reduces the
amount of time it takes to rerun the configure script with (hopefully)
the error that caused the previous abort corrected.
-- Macro: AC_CACHE_LOAD
Loads values from existing cache file, or creates a new cache file
if a cache file is not found. Called automatically from `AC_INIT'.
-- Macro: AC_CACHE_SAVE
Flushes all cached values to the cache file. Called automatically
from `AC_OUTPUT', but it can be quite useful to call
`AC_CACHE_SAVE' at key points in `configure.ac'.
For instance:
... AC_INIT, etc. ...
# Checks for programs.
AC_PROG_CC
AC_PROG_AWK
... more program checks ...
AC_CACHE_SAVE
# Checks for libraries.
AC_CHECK_LIB([nsl], [gethostbyname])
AC_CHECK_LIB([socket], [connect])
... more lib checks ...
AC_CACHE_SAVE
# Might abort...
AM_PATH_GTK([1.0.2], [], [AC_MSG_ERROR([GTK not in path])])
AM_PATH_GTKMM([0.9.5], [], [AC_MSG_ERROR([GTK not in path])])
... AC_OUTPUT, etc. ...
File: autoconf.info, Node: Printing Messages, Prev: Caching Results, Up: Results
7.5 Printing Messages
=====================
`configure' scripts need to give users running them several kinds of
information. The following macros print messages in ways appropriate
for each kind. The arguments to all of them get enclosed in shell
double quotes, so the shell performs variable and back-quote
substitution on them.
These macros are all wrappers around the `echo' shell command. They
direct output to the appropriate file descriptor (*note File Descriptor
Macros::). `configure' scripts should rarely need to run `echo'
directly to print messages for the user. Using these macros makes it
easy to change how and when each kind of message is printed; such
changes need only be made to the macro definitions and all the callers
change automatically.
To diagnose static issues, i.e., when `autoconf' is run, see *note
Diagnostic Macros::.
-- Macro: AC_MSG_CHECKING (FEATURE-DESCRIPTION)
Notify the user that `configure' is checking for a particular
feature. This macro prints a message that starts with `checking '
and ends with `...' and no newline. It must be followed by a call
to `AC_MSG_RESULT' to print the result of the check and the
newline. The FEATURE-DESCRIPTION should be something like
`whether the Fortran compiler accepts C++ comments' or `for c89'.
This macro prints nothing if `configure' is run with the `--quiet'
or `--silent' option.
-- Macro: AC_MSG_RESULT (RESULT-DESCRIPTION)
Notify the user of the results of a check. RESULT-DESCRIPTION is
almost always the value of the cache variable for the check,
typically `yes', `no', or a file name. This macro should follow a
call to `AC_MSG_CHECKING', and the RESULT-DESCRIPTION should be
the completion of the message printed by the call to
`AC_MSG_CHECKING'.
This macro prints nothing if `configure' is run with the `--quiet'
or `--silent' option.
-- Macro: AC_MSG_NOTICE (MESSAGE)
Deliver the MESSAGE to the user. It is useful mainly to print a
general description of the overall purpose of a group of feature
checks, e.g.,
AC_MSG_NOTICE([checking if stack overflow is detectable])
This macro prints nothing if `configure' is run with the `--quiet'
or `--silent' option.
-- Macro: AC_MSG_ERROR (ERROR-DESCRIPTION, [EXIT-STATUS = `$?/1'])
Notify the user of an error that prevents `configure' from
completing. This macro prints an error message to the standard
error output and exits `configure' with EXIT-STATUS (`$?' by
default, except that `0' is converted to `1'). ERROR-DESCRIPTION
should be something like `invalid value $HOME for \$HOME'.
The ERROR-DESCRIPTION should start with a lower-case letter, and
"cannot" is preferred to "can't".
-- Macro: AC_MSG_FAILURE (ERROR-DESCRIPTION, [EXIT-STATUS])
This `AC_MSG_ERROR' wrapper notifies the user of an error that
prevents `configure' from completing _and_ that additional details
are provided in `config.log'. This is typically used when
abnormal results are found during a compilation.
-- Macro: AC_MSG_WARN (PROBLEM-DESCRIPTION)
Notify the `configure' user of a possible problem. This macro
prints the message to the standard error output; `configure'
continues running afterward, so macros that call `AC_MSG_WARN'
should provide a default (back-up) behavior for the situations
they warn about. PROBLEM-DESCRIPTION should be something like `ln
-s seems to make hard links'.
File: autoconf.info, Node: Programming in M4, Next: Programming in M4sh, Prev: Results, Up: Top
8 Programming in M4
*******************
Autoconf is written on top of two layers: "M4sugar", which provides
convenient macros for pure M4 programming, and "M4sh", which provides
macros dedicated to shell script generation.
As of this version of Autoconf, these two layers still contain
experimental macros, whose interface might change in the future. As a
matter of fact, _anything that is not documented must not be used_.
* Menu:
* M4 Quotation:: Protecting macros from unwanted expansion
* Using autom4te:: The Autoconf executables backbone
* Programming in M4sugar:: Convenient pure M4 macros
* Debugging via autom4te:: Figuring out what M4 was doing
File: autoconf.info, Node: M4 Quotation, Next: Using autom4te, Up: Programming in M4
8.1 M4 Quotation
================
The most common problem with existing macros is an improper quotation.
This section, which users of Autoconf can skip, but which macro writers
_must_ read, first justifies the quotation scheme that was chosen for
Autoconf and then ends with a rule of thumb. Understanding the former
helps one to follow the latter.
* Menu:
* Active Characters:: Characters that change the behavior of M4
* One Macro Call:: Quotation and one macro call
* Quoting and Parameters:: M4 vs. shell parameters
* Quotation and Nested Macros:: Macros calling macros
* Changequote is Evil:: Worse than INTERCAL: M4 + changequote
* Quadrigraphs:: Another way to escape special characters
* Balancing Parentheses:: Dealing with unbalanced parentheses
* Quotation Rule Of Thumb:: One parenthesis, one quote
File: autoconf.info, Node: Active Characters, Next: One Macro Call, Up: M4 Quotation
8.1.1 Active Characters
-----------------------
To fully understand where proper quotation is important, you first need
to know what the special characters are in Autoconf: `#' introduces a
comment inside which no macro expansion is performed, `,' separates
arguments, `[' and `]' are the quotes themselves(1), `(' and `)' (which
M4 tries to match by pairs), and finally `$' inside a macro definition.
In order to understand the delicate case of macro calls, we first
have to present some obvious failures. Below they are "obvious-ified",
but when you find them in real life, they are usually in disguise.
Comments, introduced by a hash and running up to the newline, are
opaque tokens to the top level: active characters are turned off, and
there is no macro expansion:
# define([def], ine)
=># define([def], ine)
Each time there can be a macro expansion, there is a quotation
expansion, i.e., one level of quotes is stripped:
int tab[10];
=>int tab10;
[int tab[10];]
=>int tab[10];
Without this in mind, the reader might try hopelessly to use her
macro `array':
define([array], [int tab[10];])
array
=>int tab10;
[array]
=>array
How can you correctly output the intended results(2)?
---------- Footnotes ----------
(1) By itself, M4 uses ``' and `''; it is the M4sugar layer that
sets up the preferred quotes of `[' and `]'.
(2) Using `defn'.
File: autoconf.info, Node: One Macro Call, Next: Quoting and Parameters, Prev: Active Characters, Up: M4 Quotation
8.1.2 One Macro Call
--------------------
Let's proceed on the interaction between active characters and macros
with this small macro, which just returns its first argument:
define([car], [$1])
The two pairs of quotes above are not part of the arguments of
`define'; rather, they are understood by the top level when it tries to
find the arguments of `define'. Therefore, assuming `car' is not
already defined, it is equivalent to write:
define(car, $1)
But, while it is acceptable for a `configure.ac' to avoid unnecessary
quotes, it is bad practice for Autoconf macros which must both be more
robust and also advocate perfect style.
At the top level, there are only two possibilities: either you quote
or you don't:
car(foo, bar, baz)
=>foo
[car(foo, bar, baz)]
=>car(foo, bar, baz)
Let's pay attention to the special characters:
car(#)
error-->EOF in argument list
The closing parenthesis is hidden in the comment; with a hypothetical
quoting, the top level understood it this way:
car([#)]
Proper quotation, of course, fixes the problem:
car([#])
=>#
Here are more examples:
car(foo, bar)
=>foo
car([foo, bar])
=>foo, bar
car((foo, bar))
=>(foo, bar)
car([(foo], [bar)])
=>(foo
define([a], [b])
=>
car(a)
=>b
car([a])
=>b
car([[a]])
=>a
car([[[a]]])
=>[a]
File: autoconf.info, Node: Quoting and Parameters, Next: Quotation and Nested Macros, Prev: One Macro Call, Up: M4 Quotation
8.1.3 Quoting and Parameters
----------------------------
When M4 encounters `$' within a macro definition, followed immediately
by a character it recognizes (`0'...`9', `#', `@', or `*'), it will
perform M4 parameter expansion. This happens regardless of how many
layers of quotes the parameter expansion is nested within, or even if
it occurs in text that will be rescanned as a comment.
define([none], [$1])
=>
define([one], [[$1]])
=>
define([two], [[[$1]]])
=>
define([comment], [# $1])
=>
define([active], [ACTIVE])
=>
none([active])
=>ACTIVE
one([active])
=>active
two([active])
=>[active]
comment([active])
=># active
On the other hand, since autoconf generates shell code, you often
want to output shell variable expansion, rather than performing M4
parameter expansion. To do this, you must use M4 quoting to separate
the `$' from the next character in the definition of your macro. If
the macro definition occurs in single-quoted text, then insert another
level of quoting; if the usage is already inside a double-quoted
string, then split it into concatenated strings.
define([single], [a single-quoted $[]1 definition])
=>
define([double], [[a double-quoted $][1 definition]])
=>
single
=>a single-quoted $1 definition
double
=>a double-quoted $1 definition
Posix states that M4 implementations are free to provide
implementation extensions when `${' is encountered in a macro
definition. Autoconf reserves the longer sequence `${{' for use with
planned extensions that will be available in the future GNU M4 2.0, but
guarantees that all other instances of `${' will be output literally.
Therefore, this idiom can also be used to output shell code parameter
references:
define([first], [${1}])first
=>${1}
Posix also states that `$11' should expand to the first parameter
concatenated with a literal `1', although some versions of GNU M4
expand the eleventh parameter instead. For portability, you should
only use single-digit M4 parameter expansion.
With this in mind, we can explore the cases where macros invoke
macros...
File: autoconf.info, Node: Quotation and Nested Macros, Next: Changequote is Evil, Prev: Quoting and Parameters, Up: M4 Quotation
8.1.4 Quotation and Nested Macros
---------------------------------
The examples below use the following macros:
define([car], [$1])
define([active], [ACT, IVE])
define([array], [int tab[10]])
Each additional embedded macro call introduces other possible
interesting quotations:
car(active)
=>ACT
car([active])
=>ACT, IVE
car([[active]])
=>active
In the first case, the top level looks for the arguments of `car',
and finds `active'. Because M4 evaluates its arguments before applying
the macro, `active' is expanded, which results in:
car(ACT, IVE)
=>ACT
In the second case, the top level gives `active' as first and only
argument of `car', which results in:
active
=>ACT, IVE
i.e., the argument is evaluated _after_ the macro that invokes it. In
the third case, `car' receives `[active]', which results in:
[active]
=>active
exactly as we already saw above.
The example above, applied to a more realistic example, gives:
car(int tab[10];)
=>int tab10;
car([int tab[10];])
=>int tab10;
car([[int tab[10];]])
=>int tab[10];
Huh? The first case is easily understood, but why is the second wrong,
and the third right? To understand that, you must know that after M4
expands a macro, the resulting text is immediately subjected to macro
expansion and quote removal. This means that the quote removal occurs
twice--first before the argument is passed to the `car' macro, and
second after the `car' macro expands to the first argument.
As the author of the Autoconf macro `car', you then consider it to
be incorrect that your users have to double-quote the arguments of
`car', so you "fix" your macro. Let's call it `qar' for quoted car:
define([qar], [[$1]])
and check that `qar' is properly fixed:
qar([int tab[10];])
=>int tab[10];
Ahhh! That's much better.
But note what you've done: now that the result of `qar' is always a
literal string, the only time a user can use nested macros is if she
relies on an _unquoted_ macro call:
qar(active)
=>ACT
qar([active])
=>active
leaving no way for her to reproduce what she used to do with `car':
car([active])
=>ACT, IVE
Worse yet: she wants to use a macro that produces a set of `cpp' macros:
define([my_includes], [#include ])
car([my_includes])
=>#include
qar(my_includes)
error-->EOF in argument list
This macro, `qar', because it double quotes its arguments, forces
its users to leave their macro calls unquoted, which is dangerous.
Commas and other active symbols are interpreted by M4 before they are
given to the macro, often not in the way the users expect. Also,
because `qar' behaves differently from the other macros, it's an
exception that should be avoided in Autoconf.
File: autoconf.info, Node: Changequote is Evil, Next: Quadrigraphs, Prev: Quotation and Nested Macros, Up: M4 Quotation
8.1.5 `changequote' is Evil
---------------------------
The temptation is often high to bypass proper quotation, in particular
when it's late at night. Then, many experienced Autoconf hackers
finally surrender to the dark side of the force and use the ultimate
weapon: `changequote'.
The M4 builtin `changequote' belongs to a set of primitives that
allow one to adjust the syntax of the language to adjust it to one's
needs. For instance, by default M4 uses ``' and `'' as quotes, but in
the context of shell programming (and actually of most programming
languages), that's about the worst choice one can make: because of
strings and back-quoted expressions in shell code (such as `'this'' and
``that`'), and because of literal characters in usual programming
languages (as in `'0''), there are many unbalanced ``' and `''. Proper
M4 quotation then becomes a nightmare, if not impossible. In order to
make M4 useful in such a context, its designers have equipped it with
`changequote', which makes it possible to choose another pair of
quotes. M4sugar, M4sh, Autoconf, and Autotest all have chosen to use
`[' and `]'. Not especially because they are unlikely characters, but
_because they are characters unlikely to be unbalanced_.
There are other magic primitives, such as `changecom' to specify
what syntactic forms are comments (it is common to see `changecom()' when M4 is used to produce HTML pages), `changeword' and
`changesyntax' to change other syntactic details (such as the character
to denote the Nth argument, `$' by default, the parentheses around
arguments, etc.).
These primitives are really meant to make M4 more useful for specific
domains: they should be considered like command line options:
`--quotes', `--comments', `--words', and `--syntax'. Nevertheless,
they are implemented as M4 builtins, as it makes M4 libraries self
contained (no need for additional options).
There lies the problem...
The problem is that it is then tempting to use them in the middle of
an M4 script, as opposed to its initialization. This, if not carefully
thought out, can lead to disastrous effects: _you are changing the
language in the middle of the execution_. Changing and restoring the
syntax is often not enough: if you happened to invoke macros in between,
these macros are lost, as the current syntax is probably not the one
they were implemented with.
File: autoconf.info, Node: Quadrigraphs, Next: Balancing Parentheses, Prev: Changequote is Evil, Up: M4 Quotation
8.1.6 Quadrigraphs
------------------
When writing an Autoconf macro you may occasionally need to generate
special characters that are difficult to express with the standard
Autoconf quoting rules. For example, you may need to output the regular
expression `[^[]', which matches any character other than `['. This
expression contains unbalanced brackets so it cannot be put easily into
an M4 macro.
Additionally, there are a few m4sugar macros (such as `m4_split' and
`m4_expand') which internally use special markers in addition to the
regular quoting characters. If the arguments to these macros contain
the literal strings `-==-', the macros might behave
incorrectly.
You can work around these problems by using one of the following
"quadrigraphs":
`@@'
`]'
`@S|@'
`$'
`@%:@'
`#'
`@{:@'
`('
`@:}@'
`)'
`@&t@'
Expands to nothing.
Quadrigraphs are replaced at a late stage of the translation process,
after `m4' is run, so they do not get in the way of M4 quoting. For
example, the string `^@=- b -=[a], [], [B], [], [c]
m4_split([a )}@&t@>=- b -=[a], [)}>=-], [b], [-=
File: autoconf.info, Node: Balancing Parentheses, Next: Quotation Rule Of Thumb, Prev: Quadrigraphs, Up: M4 Quotation
8.1.7 Dealing with unbalanced parentheses
-----------------------------------------
One of the pitfalls of portable shell programming is that `case'
statements require unbalanced parentheses (*note Limitations of Shell
Builtins: case.). With syntax highlighting editors, the presence of
unbalanced `)' can interfere with editors that perform syntax
highlighting of macro contents based on finding the matching `('.
Another concern is how much editing must be done when transferring code
snippets between shell scripts and macro definitions. But most
importantly, the presence of unbalanced parentheses can introduce
expansion bugs.
For an example, here is an underquoted attempt to use the macro
`my_case', which happens to expand to a portable `case' statement:
AC_DEFUN([my_case],
[case $file_name in
*.c) echo "C source code";;
esac])
AS_IF(:, my_case)
In the above example, the `AS_IF' call underquotes its arguments. As a
result, the unbalanced `)' generated by the premature expansion of
`my_case' results in expanding `AS_IF' with a truncated parameter, and
the expansion is syntactically invalid:
if :; then
case $file_name in
*.c
fi echo "C source code";;
esac)
If nothing else, this should emphasize the importance of the quoting
arguments to macro calls. On the other hand, there are several
variations for defining `my_case' to be more robust, even when used
without proper quoting, each with some benefits and some drawbacks.
Creative literal shell comment
AC_DEFUN([my_case],
[case $file_name in #(
*.c) echo "C source code";;
esac])
This version provides balanced parentheses to several editors, and
can be copied and pasted into a terminal as is. Unfortunately, it
is still unbalanced as an Autoconf argument, since `#(' is an M4
comment that masks the normal properties of `('.
Quadrigraph shell comment
AC_DEFUN([my_case],
[case $file_name in @%:@(
*.c) echo "C source code";;
esac])
This version provides balanced parentheses to even more editors,
and can be used as a balanced Autoconf argument. Unfortunately,
it requires some editing before it can be copied and pasted into a
terminal, and the use of the quadrigraph `@%:@' for `#' reduces
readability.
Quoting just the parenthesis
AC_DEFUN([my_case],
[case $file_name in
*.c[)] echo "C source code";;
esac])
This version quotes the `)', so that it can be used as a balanced
Autoconf argument. As written, this is not balanced to an editor,
but it can be coupled with `[#(]' to meet that need, too.
However, it still requires some edits before it can be copied and
pasted into a terminal.
Double-quoting the entire statement
AC_DEFUN([my_case],
[[case $file_name in #(
*.c) echo "C source code";;
esac]])
Since the entire macro is double-quoted, there is no problem with
using this as an Autoconf argument; and since the double-quoting
is over the entire statement, this code can be easily copied and
pasted into a terminal. However, the double quoting prevents the
expansion of any macros inside the case statement, which may cause
its own set of problems.
Using `AS_CASE'
AC_DEFUN([my_case],
[AS_CASE([$file_name],
[*.c], [echo "C source code"])])
This version avoids the balancing issue altogether, by relying on
`AS_CASE' (*note Common Shell Constructs::); it also allows for the
expansion of `AC_REQUIRE' to occur prior to the entire case
statement, rather than within a branch of the case statement that
might not be taken. However, the abstraction comes with a penalty
that it is no longer a quick copy, paste, and edit to get back to
shell code.
File: autoconf.info, Node: Quotation Rule Of Thumb, Prev: Balancing Parentheses, Up: M4 Quotation
8.1.8 Quotation Rule Of Thumb
-----------------------------
To conclude, the quotation rule of thumb is:
_One pair of quotes per pair of parentheses._
Never over-quote, never under-quote, in particular in the definition
of macros. In the few places where the macros need to use brackets
(usually in C program text or regular expressions), properly quote _the
arguments_!
It is common to read Autoconf programs with snippets like:
AC_TRY_LINK(
changequote(<>)dnl
<
#ifndef tzname /* For SGI. */
extern char *tzname[]; /* RS6000 and others reject char **tzname. */
#endif>>,
changequote([, ])dnl
[atoi (*tzname);], ac_cv_var_tzname=yes, ac_cv_var_tzname=no)
which is incredibly useless since `AC_TRY_LINK' is _already_ double
quoting, so you just need:
AC_TRY_LINK(
[#include
#ifndef tzname /* For SGI. */
extern char *tzname[]; /* RS6000 and others reject char **tzname. */
#endif],
[atoi (*tzname);],
[ac_cv_var_tzname=yes],
[ac_cv_var_tzname=no])
The M4-fluent reader might note that these two examples are rigorously
equivalent, since M4 swallows both the `changequote(<>)' and `<>' when it "collects" the arguments: these quotes are not part of the
arguments!
Simplified, the example above is just doing this:
changequote(<>)dnl
<>
changequote([, ])dnl
instead of simply:
[[]]
With macros that do not double quote their arguments (which is the
rule), double-quote the (risky) literals:
AC_LINK_IFELSE([AC_LANG_PROGRAM(
[[#include
#ifndef tzname /* For SGI. */
extern char *tzname[]; /* RS6000 and others reject char **tzname. */
#endif]],
[atoi (*tzname);])],
[ac_cv_var_tzname=yes],
[ac_cv_var_tzname=no])
Please note that the macro `AC_TRY_LINK' is obsolete, so you really
should be using `AC_LINK_IFELSE' instead.
*Note Quadrigraphs::, for what to do if you run into a hopeless case
where quoting does not suffice.
When you create a `configure' script using newly written macros,
examine it carefully to check whether you need to add more quotes in
your macros. If one or more words have disappeared in the M4 output,
you need more quotes. When in doubt, quote.
However, it's also possible to put on too many layers of quotes. If
this happens, the resulting `configure' script may contain unexpanded
macros. The `autoconf' program checks for this problem by looking for
the string `AC_' in `configure'. However, this heuristic does not work
in general: for example, it does not catch overquoting in `AC_DEFINE'
descriptions.
File: autoconf.info, Node: Using autom4te, Next: Programming in M4sugar, Prev: M4 Quotation, Up: Programming in M4
8.2 Using `autom4te'
====================
The Autoconf suite, including M4sugar, M4sh, and Autotest, in addition
to Autoconf per se, heavily rely on M4. All these different uses
revealed common needs factored into a layer over M4: `autom4te'(1).
`autom4te' is a preprocessor that is like `m4'. It supports M4
extensions designed for use in tools like Autoconf.
* Menu:
* autom4te Invocation:: A GNU M4 wrapper
* Customizing autom4te:: Customizing the Autoconf package
---------- Footnotes ----------
(1) Yet another great name from Lars J. Aas.
File: autoconf.info, Node: autom4te Invocation, Next: Customizing autom4te, Up: Using autom4te
8.2.1 Invoking `autom4te'
-------------------------
The command line arguments are modeled after M4's:
autom4te OPTIONS FILES
where the FILES are directly passed to `m4'. By default, GNU M4 is
found during configuration, but the environment variable `M4' can be
set to tell `autom4te' where to look. In addition to the regular
expansion, it handles the replacement of the quadrigraphs (*note
Quadrigraphs::), and of `__oline__', the current line in the output.
It supports an extended syntax for the FILES:
`FILE.m4f'
This file is an M4 frozen file. Note that _all the previous files
are ignored_. See the option `--melt' for the rationale.
`FILE?'
If found in the library path, the FILE is included for expansion,
otherwise it is ignored instead of triggering a failure.
Of course, it supports the Autoconf common subset of options:
`--help'
`-h'
Print a summary of the command line options and exit.
`--version'
`-V'
Print the version number of Autoconf and exit.
`--verbose'
`-v'
Report processing steps.
`--debug'
`-d'
Don't remove the temporary files and be even more verbose.
`--include=DIR'
`-I DIR'
Also look for input files in DIR. Multiple invocations accumulate.
`--output=FILE'
`-o FILE'
Save output (script or trace) to FILE. The file `-' stands for
the standard output.
As an extension of `m4', it includes the following options:
`--warnings=CATEGORY'
`-W CATEGORY'
Report the warnings related to CATEGORY (which can actually be a
comma separated list). *Note Reporting Messages::, macro
`AC_DIAGNOSE', for a comprehensive list of categories. Special
values include:
`all'
report all the warnings
`none'
report none
`error'
treats warnings as errors
`no-CATEGORY'
disable warnings falling into CATEGORY
Warnings about `syntax' are enabled by default, and the environment
variable `WARNINGS', a comma separated list of categories, is
honored. `autom4te -W CATEGORY' actually behaves as if you had
run:
autom4te --warnings=syntax,$WARNINGS,CATEGORY
For example, if you want to disable defaults and `WARNINGS' of
`autom4te', but enable the warnings about obsolete constructs, you
would use `-W none,obsolete'.
`autom4te' displays a back trace for errors, but not for warnings;
if you want them, just pass `-W error'.
`--melt'
`-M'
Do not use frozen files. Any argument `FILE.m4f' is replaced by
`FILE.m4'. This helps tracing the macros which are executed only
when the files are frozen, typically `m4_define'. For instance,
running:
autom4te --melt 1.m4 2.m4f 3.m4 4.m4f input.m4
is roughly equivalent to running:
m4 1.m4 2.m4 3.m4 4.m4 input.m4
while
autom4te 1.m4 2.m4f 3.m4 4.m4f input.m4
is equivalent to:
m4 --reload-state=4.m4f input.m4
`--freeze'
`-F'
Produce a frozen state file. `autom4te' freezing is stricter than
M4's: it must produce no warnings, and no output other than empty
lines (a line with white space is _not_ empty) and comments
(starting with `#'). Unlike `m4''s similarly-named option, this
option takes no argument:
autom4te 1.m4 2.m4 3.m4 --freeze --output=3.m4f
corresponds to
m4 1.m4 2.m4 3.m4 --freeze-state=3.m4f
`--mode=OCTAL-MODE'
`-m OCTAL-MODE'
Set the mode of the non-traces output to OCTAL-MODE; by default
`0666'.
As another additional feature over `m4', `autom4te' caches its
results. GNU M4 is able to produce a regular output and traces at the
same time. Traces are heavily used in the GNU Build System:
`autoheader' uses them to build `config.h.in', `autoreconf' to
determine what GNU Build System components are used, `automake' to
"parse" `configure.ac' etc. To avoid recomputation, traces are cached
while performing regular expansion, and conversely. This cache is
(actually, the caches are) stored in the directory `autom4te.cache'.
_It can safely be removed_ at any moment (especially if for some reason
`autom4te' considers it trashed).
`--cache=DIRECTORY'
`-C DIRECTORY'
Specify the name of the directory where the result should be
cached. Passing an empty value disables caching. Be sure to pass
a relative file name, as for the time being, global caches are not
supported.
`--no-cache'
Don't cache the results.
`--force'
`-f'
If a cache is used, consider it obsolete (but update it anyway).
Because traces are so important to the GNU Build System, `autom4te'
provides high level tracing features as compared to M4, and helps
exploiting the cache:
`--trace=MACRO[:FORMAT]'
`-t MACRO[:FORMAT]'
Trace the invocations of MACRO according to the FORMAT. Multiple
`--trace' arguments can be used to list several macros. Multiple
`--trace' arguments for a single macro are not cumulative;
instead, you should just make FORMAT as long as needed.
The FORMAT is a regular string, with newlines if desired, and
several special escape codes. It defaults to `$f:$l:$n:$%'. It
can use the following special escapes:
`$$'
The character `$'.
`$f'
The file name from which MACRO is called.
`$l'
The line number from which MACRO is called.
`$d'
The depth of the MACRO call. This is an M4 technical detail
that you probably don't want to know about.
`$n'
The name of the MACRO.
`$NUM'
The NUMth argument of the call to MACRO.
`$@'
`$SEP@'
`${SEPARATOR}@'
All the arguments passed to MACRO, separated by the character
SEP or the string SEPARATOR (`,' by default). Each argument
is quoted, i.e., enclosed in a pair of square brackets.
`$*'
`$SEP*'
`${SEPARATOR}*'
As above, but the arguments are not quoted.
`$%'
`$SEP%'
`${SEPARATOR}%'
As above, but the arguments are not quoted, all new line
characters in the arguments are smashed, and the default
separator is `:'.
The escape `$%' produces single-line trace outputs (unless
you put newlines in the `separator'), while `$@' and `$*' do
not.
*Note autoconf Invocation::, for examples of trace uses.
`--preselect=MACRO'
`-p MACRO'
Cache the traces of MACRO, but do not enable traces. This is
especially important to save CPU cycles in the future. For
instance, when invoked, `autoconf' preselects all the macros that
`autoheader', `automake', `autoreconf', etc., trace, so that
running `m4' is not needed to trace them: the cache suffices.
This results in a huge speed-up.
Finally, `autom4te' introduces the concept of "Autom4te libraries".
They consists in a powerful yet extremely simple feature: sets of
combined command line arguments:
`--language=LANGUAGE'
`-l LANGUAGE'
Use the LANGUAGE Autom4te library. Current languages include:
`M4sugar'
create M4sugar output.
`M4sh'
create M4sh executable shell scripts.
`Autotest'
create Autotest executable test suites.
`Autoconf-without-aclocal-m4'
create Autoconf executable configure scripts without reading
`aclocal.m4'.
`Autoconf'
create Autoconf executable configure scripts. This language
inherits all the characteristics of
`Autoconf-without-aclocal-m4' and additionally reads
`aclocal.m4'.
`--prepend-include=DIR'
`-B DIR'
Prepend directory DIR to the search path. This is used to include
the language-specific files before any third-party macros.
As an example, if Autoconf is installed in its default location,
`/usr/local', the command `autom4te -l m4sugar foo.m4' is strictly
equivalent to the command:
autom4te --prepend-include /usr/local/share/autoconf \
m4sugar/m4sugar.m4f --warnings syntax foo.m4
Recursive expansion applies here: the command `autom4te -l m4sh foo.m4'
is the same as `autom4te --language M4sugar m4sugar/m4sh.m4f foo.m4',
i.e.:
autom4te --prepend-include /usr/local/share/autoconf \
m4sugar/m4sugar.m4f m4sugar/m4sh.m4f --mode 777 foo.m4
The definition of the languages is stored in `autom4te.cfg'.
File: autoconf.info, Node: Customizing autom4te, Prev: autom4te Invocation, Up: Using autom4te
8.2.2 Customizing `autom4te'
----------------------------
One can customize `autom4te' via `~/.autom4te.cfg' (i.e., as found in
the user home directory), and `./.autom4te.cfg' (i.e., as found in the
directory from which `autom4te' is run). The order is first reading
`autom4te.cfg', then `~/.autom4te.cfg', then `./.autom4te.cfg', and
finally the command line arguments.
In these text files, comments are introduced with `#', and empty
lines are ignored. Customization is performed on a per-language basis,
wrapped in between a `begin-language: "LANGUAGE"', `end-language:
"LANGUAGE"' pair.
Customizing a language stands for appending options (*note autom4te
Invocation::) to the current definition of the language. Options, and
more generally arguments, are introduced by `args: ARGUMENTS'. You may
use the traditional shell syntax to quote the ARGUMENTS.
As an example, to disable Autoconf caches (`autom4te.cache')
globally, include the following lines in `~/.autom4te.cfg':
## ------------------ ##
## User Preferences. ##
## ------------------ ##
begin-language: "Autoconf-without-aclocal-m4"
args: --no-cache
end-language: "Autoconf-without-aclocal-m4"
File: autoconf.info, Node: Programming in M4sugar, Next: Debugging via autom4te, Prev: Using autom4te, Up: Programming in M4
8.3 Programming in M4sugar
==========================
M4 by itself provides only a small, but sufficient, set of all-purpose
macros. M4sugar introduces additional generic macros. Its name was
coined by Lars J. Aas: "Readability And Greater Understanding Stands 4
M4sugar".
M4sugar reserves the macro namespace `^_m4_' for internal use, and
the macro namespace `^m4_' for M4sugar macros. You should not define
your own macros into these namespaces.
* Menu:
* Redefined M4 Macros:: M4 builtins changed in M4sugar
* Diagnostic Macros:: Diagnostic messages from M4sugar
* Diversion support:: Diversions in M4sugar
* Conditional constructs:: Conditions in M4
* Looping constructs:: Iteration in M4
* Evaluation Macros:: More quotation and evaluation control
* Text processing Macros:: String manipulation in M4
* Number processing Macros:: Arithmetic computation in M4
* Set manipulation Macros:: Set manipulation in M4
* Forbidden Patterns:: Catching unexpanded macros
File: autoconf.info, Node: Redefined M4 Macros, Next: Diagnostic Macros, Up: Programming in M4sugar
8.3.1 Redefined M4 Macros
-------------------------
With a few exceptions, all the M4 native macros are moved in the `m4_'
pseudo-namespace, e.g., M4sugar renames `define' as `m4_define' etc.
The list of macros unchanged from M4, except for their name, is:
- m4_builtin
- m4_changecom
- m4_changequote
- m4_debugfile
- m4_debugmode
- m4_decr
- m4_define
- m4_divnum
- m4_errprint
- m4_esyscmd
- m4_eval
- m4_format
- m4_ifdef
- m4_incr
- m4_index
- m4_indir
- m4_len
- m4_pushdef
- m4_shift
- m4_substr
- m4_syscmd
- m4_sysval
- m4_traceoff
- m4_traceon
- m4_translit
Some M4 macros are redefined, and are slightly incompatible with
their native equivalent.
-- Macro: __file__
-- Macro: __line__
All M4 macros starting with `__' retain their original name: for
example, no `m4__file__' is defined.
-- Macro: __oline__
This is not technically a macro, but a feature of Autom4te. The
sequence `__oline__' can be used similarly to the other m4sugar
location macros, but rather than expanding to the location of the
input file, it is translated to the line number where it appears
in the output file after all other M4 expansions.
-- Macro: dnl
This macro kept its original name: no `m4_dnl' is defined.
-- Macro: m4_bpatsubst (STRING, REGEXP, [REPLACEMENT])
This macro corresponds to `patsubst'. The name `m4_patsubst' is
kept for future versions of M4sugar, once GNU M4 2.0 is released
and supports extended regular expression syntax.
-- Macro: m4_bregexp (STRING, REGEXP, [REPLACEMENT])
This macro corresponds to `regexp'. The name `m4_regexp' is kept
for future versions of M4sugar, once GNU M4 2.0 is released and
supports extended regular expression syntax.
-- Macro: m4_copy (SOURCE, DEST)
-- Macro: m4_copy_force (SOURCE, DEST)
-- Macro: m4_rename (SOURCE, DEST)
-- Macro: m4_rename_force (SOURCE, DEST)
These macros aren't directly builtins, but are closely related to
`m4_pushdef' and `m4_defn'. `m4_copy' and `m4_rename' ensure that
DEST is undefined, while `m4_copy_force' and `m4_rename_force'
overwrite any existing definition. All four macros then proceed
to copy the entire pushdef stack of definitions of SOURCE over to
DEST. `m4_copy' and `m4_copy_force' preserve the source
(including in the special case where SOURCE is undefined), while
`m4_rename' and `m4_rename_force' undefine the original macro name
(making it an error to rename an undefined SOURCE).
Note that attempting to invoke a renamed macro might not work,
since the macro may have a dependence on helper macros accessed
via composition of `$0' but that were not also renamed; likewise,
other macros may have a hard-coded dependence on SOURCE and could
break if SOURCE has been deleted. On the other hand, it is always
safe to rename a macro to temporarily move it out of the way, then
rename it back later to restore original semantics.
-- Macro: m4_defn (MACRO...)
This macro fails if MACRO is not defined, even when using older
versions of M4 that did not warn. See `m4_undefine'.
Unfortunately, in order to support these older versions of M4,
there are some situations involving unbalanced quotes where
concatenating multiple macros together will work in newer M4 but
not in m4sugar; use quadrigraphs to work around this.
-- Macro: m4_divert (DIVERSION)
M4sugar relies heavily on diversions, so rather than behaving as a
primitive, `m4_divert' behaves like:
m4_divert_pop()m4_divert_push([DIVERSION])
*Note Diversion support::, for more details about the use of the
diversion stack. In particular, this implies that DIVERSION
should be a named diversion rather than a raw number. But be
aware that it is seldom necessary to explicitly change the
diversion stack, and that when done incorrectly, it can lead to
syntactically invalid scripts.
-- Macro: m4_dumpdef (NAME...)
-- Macro: m4_dumpdefs (NAME...)
`m4_dumpdef' is like the M4 builtin, except that this version
requires at least one argument, output always goes to standard
error rather than the current debug file, no sorting is done on
multiple arguments, and an error is issued if any NAME is
undefined. `m4_dumpdefs' is a convenience macro that calls
`m4_dumpdef' for all of the `m4_pushdef' stack of definitions,
starting with the current, and silently does nothing if NAME is
undefined.
Unfortunately, due to a limitation in M4 1.4.x, any macro defined
as a builtin is output as the empty string. This behavior is
rectified by using M4 1.6 or newer. However, this behavior
difference means that `m4_dumpdef' should only be used while
developing m4sugar macros, and never in the final published form
of a macro.
-- Macro: m4_esyscmd_s (COMMAND)
Like `m4_esyscmd', this macro expands to the result of running
COMMAND in a shell. The difference is that any trailing newlines
are removed, so that the output behaves more like shell command
substitution.
-- Macro: m4_exit (EXIT-STATUS)
This macro corresponds to `m4exit'.
-- Macro: m4_if (COMMENT)
-- Macro: m4_if (STRING-1, STRING-2, EQUAL, [NOT-EQUAL])
-- Macro: m4_if (STRING-1, STRING-2, EQUAL-1, STRING-3, STRING-4,
EQUAL-2, ..., [NOT-EQUAL])
This macro corresponds to `ifelse'. STRING-1 and STRING-2 are
compared literally, so usually one of the two arguments is passed
unquoted. *Note Conditional constructs::, for more conditional
idioms.
-- Macro: m4_include (FILE)
-- Macro: m4_sinclude (FILE)
Like the M4 builtins, but warn against multiple inclusions of FILE.
-- Macro: m4_mkstemp (TEMPLATE)
-- Macro: m4_maketemp (TEMPLATE)
Posix requires `maketemp' to replace the trailing `X' characters
in TEMPLATE with the process id, without regards to the existence
of a file by that name, but this a security hole. When this was
pointed out to the Posix folks, they agreed to invent a new macro
`mkstemp' that always creates a uniquely named file, but not all
versions of GNU M4 support the new macro. In M4sugar,
`m4_maketemp' and `m4_mkstemp' are synonyms for each other, and
both have the secure semantics regardless of which macro the
underlying M4 provides.
-- Macro: m4_popdef (MACRO...)
This macro fails if MACRO is not defined, even when using older
versions of M4 that did not warn. See `m4_undefine'.
-- Macro: m4_undefine (MACRO...)
This macro fails if MACRO is not defined, even when using older
versions of M4 that did not warn. Use
m4_ifdef([MACRO], [m4_undefine([MACRO])])
if you are not sure whether MACRO is defined.
-- Macro: m4_undivert (DIVERSION...)
Unlike the M4 builtin, at least one DIVERSION must be specified.
Also, since the M4sugar diversion stack prefers named diversions,
the use of `m4_undivert' to include files is risky. *Note
Diversion support::, for more details about the use of the
diversion stack. But be aware that it is seldom necessary to
explicitly change the diversion stack, and that when done
incorrectly, it can lead to syntactically invalid scripts.
-- Macro: m4_wrap (TEXT)
-- Macro: m4_wrap_lifo (TEXT)
These macros correspond to `m4wrap'. Posix requires arguments of
multiple wrap calls to be reprocessed at EOF in the same order as
the original calls (first-in, first-out). GNU M4 versions through
1.4.10, however, reprocess them in reverse order (last-in,
first-out). Both orders are useful, therefore, you can rely on
`m4_wrap' to provide FIFO semantics and `m4_wrap_lifo' for LIFO
semantics, regardless of the underlying GNU M4 version.
Unlike the GNU M4 builtin, these macros only recognize one
argument, and avoid token pasting between consecutive invocations.
On the other hand, nested calls to `m4_wrap' from within wrapped
text work just as in the builtin.
File: autoconf.info, Node: Diagnostic Macros, Next: Diversion support, Prev: Redefined M4 Macros, Up: Programming in M4sugar
8.3.2 Diagnostic messages from M4sugar
--------------------------------------
When macros statically diagnose abnormal situations, benign or fatal,
they should report them using these macros. For issuing dynamic issues,
i.e., when `configure' is run, see *note Printing Messages::.
-- Macro: m4_assert (EXPRESSION, [EXIT-STATUS = `1'])
Assert that the arithmetic EXPRESSION evaluates to non-zero.
Otherwise, issue a fatal error, and exit `autom4te' with
EXIT-STATUS.
-- Macro: m4_errprintn (MESSAGE)
Similar to the builtin `m4_errprint', except that a newline is
guaranteed after MESSAGE.
-- Macro: m4_fatal (MESSAGE)
Report a severe error MESSAGE prefixed with the current location,
and have `autom4te' die.
-- Macro: m4_location
Useful as a prefix in a message line. Short for:
__file__:__line__
-- Macro: m4_warn (CATEGORY, MESSAGE)
Report MESSAGE as a warning (or as an error if requested by the
user) if warnings of the CATEGORY are turned on. If the message
is emitted, it is prefixed with the current location, and followed
by a call trace of all macros defined via `AC_DEFUN' used to get
to the current expansion. You are encouraged to use standard
categories, which currently include:
`all'
messages that don't fall into one of the following
categories. Use of an empty CATEGORY is equivalent.
`cross'
related to cross compilation issues.
`obsolete'
use of an obsolete construct.
`syntax'
dubious syntactic constructs, incorrectly ordered macro calls.
File: autoconf.info, Node: Diversion support, Next: Conditional constructs, Prev: Diagnostic Macros, Up: Programming in M4sugar
8.3.3 Diversion support
-----------------------
M4sugar makes heavy use of diversions under the hood, because it is
often the case that text that must appear early in the output is not
discovered until late in the input. Additionally, some of the
topological sorting algorithms used in resolving macro dependencies use
diversions. However, most macros should not need to change diversions
directly, but rather rely on higher-level M4sugar macros to manage
diversions transparently. If you change diversions improperly, you
risk generating a syntactically invalid script, because an incorrect
diversion will violate assumptions made by many macros about whether
prerequisite text has been previously output. In short, if you
manually change the diversion, you should not expect any macros
provided by the Autoconf package to work until you have restored the
diversion stack back to its original state.
In the rare case that it is necessary to write a macro that
explicitly outputs text to a different diversion, it is important to be
aware of an M4 limitation regarding diversions: text only goes to a
diversion if it is not part of argument collection. Therefore, any
macro that changes the current diversion cannot be used as an unquoted
argument to another macro, but must be expanded at the top level. The
macro `m4_expand' will diagnose any attempt to change diversions, since
it is generally useful only as an argument to another macro. The
following example shows what happens when diversion manipulation is
attempted within macro arguments:
m4_do([normal text]
m4_divert_push([KILL])unwanted[]m4_divert_pop([KILL])
[m4_divert_push([KILL])discarded[]m4_divert_pop([KILL])])dnl
=>normal text
=>unwanted
Notice that the unquoted text `unwanted' is output, even though it was
processed while the current diversion was `KILL', because it was
collected as part of the argument to `m4_do'. However, the text
`discarded' disappeared as desired, because the diversion changes were
single-quoted, and were not expanded until the top-level rescan of the
output of `m4_do'.
To make diversion management easier, M4sugar uses the concept of
named diversions. Rather than using diversion numbers directly, it is
nicer to associate a name with each diversion. The diversion number
associated with a particular diversion name is an implementation
detail, and a syntax warning is issued if a diversion number is used
instead of a name. In general, you should not output text to a named
diversion until after calling the appropriate initialization routine
for your language (`m4_init', `AS_INIT', `AT_INIT', ...), although
there are some exceptions documented below.
M4sugar defines two named diversions.
`KILL'
Text written to this diversion is discarded. This is the default
diversion once M4sugar is initialized.
`GROW'
This diversion is used behind the scenes by topological sorting
macros, such as `AC_REQUIRE'.
M4sh adds several more named diversions.
`BINSH'
This diversion is reserved for the `#!' interpreter line.
`HEADER-REVISION'
This diversion holds text from `AC_REVISION'.
`HEADER-COMMENT'
This diversion holds comments about the purpose of a file.
`HEADER-COPYRIGHT'
This diversion is managed by `AC_COPYRIGHT'.
`M4SH-SANITIZE'
This diversion contains M4sh sanitization code, used to ensure
M4sh is executing in a reasonable shell environment.
`M4SH-INIT'
This diversion contains M4sh initialization code, initializing
variables that are required by other M4sh macros.
`BODY'
This diversion contains the body of the shell code, and is the
default diversion once M4sh is initialized.
Autotest inherits diversions from M4sh, and changes the default
diversion from `BODY' back to `KILL'. It also adds several more named
diversions, with the following subset designed for developer use.
`PREPARE_TESTS'
This diversion contains initialization sequences which are executed
after `atconfig' and `atlocal', and after all command line
arguments have been parsed, but prior to running any tests. It
can be used to set up state that is required across all tests.
This diversion will work even before `AT_INIT'.
Autoconf inherits diversions from M4sh, and adds the following named
diversions which developers can utilize.
`DEFAULTS'
This diversion contains shell variable assignments to set defaults
that must be in place before arguments are parsed. This diversion
is placed early enough in `configure' that it is unsafe to expand
any autoconf macros into this diversion.
`HELP_ENABLE'
If `AC_PRESERVE_HELP_ORDER' was used, then text placed in this
diversion will be included as part of a quoted here-doc providing
all of the `--help' output of `configure' related to options
created by `AC_ARG_WITH' and `AC_ARG_ENABLE'.
`INIT_PREPARE'
This diversion occurs after all command line options have been
parsed, but prior to the main body of the `configure' script. This
diversion is the last chance to insert shell code such as variable
assignments or shell function declarations that will used by the
expansion of other macros.
For now, the remaining named diversions of Autoconf, Autoheader, and
Autotest are not documented. In other words, intentionally outputting
text into an undocumented diversion is subject to breakage in a future
release of Autoconf.
-- Macro: m4_cleardivert (DIVERSION...)
Permanently discard any text that has been diverted into DIVERSION.
-- Macro: m4_divert_once (DIVERSION, [CONTENT])
Similar to `m4_divert_text', except that CONTENT is only output to
DIVERSION if this is the first time that `m4_divert_once' has been
called with its particular arguments.
-- Macro: m4_divert_pop ([DIVERSION])
If provided, check that the current diversion is indeed DIVERSION.
Then change to the diversion located earlier on the stack, giving
an error if an attempt is made to pop beyond the initial m4sugar
diversion of `KILL'.
-- Macro: m4_divert_push (DIVERSION)
Remember the former diversion on the diversion stack, and output
subsequent text into DIVERSION. M4sugar maintains a diversion
stack, and issues an error if there is not a matching pop for every
push.
-- Macro: m4_divert_text (DIVERSION, [CONTENT])
Output CONTENT and a newline into DIVERSION, without affecting the
current diversion. Shorthand for:
m4_divert_push([DIVERSION])CONTENT
m4_divert_pop([DIVERSION])dnl
One use of `m4_divert_text' is to develop two related macros, where
macro `MY_A' does the work, but adjusts what work is performed
based on whether the optional macro `MY_B' has also been expanded.
Of course, it is possible to use `AC_BEFORE' within `MY_A' to
require that `MY_B' occurs first, if it occurs at all. But this
imposes an ordering restriction on the user; it would be nicer if
macros `MY_A' and `MY_B' can be invoked in either order. The trick
is to let `MY_B' leave a breadcrumb in an early diversion, which
`MY_A' can then use to determine whether `MY_B' has been expanded.
AC_DEFUN([MY_A],
[# various actions
if test -n "$b_was_used"; then
# extra action
fi])
AC_DEFUN([MY_B],
[AC_REQUIRE([MY_A])dnl
m4_divert_text([INIT_PREPARE], [b_was_used=true])])
-- Macro: m4_init
Initialize the M4sugar environment, setting up the default named
diversion to be `KILL'.
File: autoconf.info, Node: Conditional constructs, Next: Looping constructs, Prev: Diversion support, Up: Programming in M4sugar
8.3.4 Conditional constructs
----------------------------
The following macros provide additional conditional constructs as
convenience wrappers around `m4_if'.
-- Macro: m4_bmatch (STRING, REGEX-1, VALUE-1, [REGEX-2], [VALUE-2],
..., [DEFAULT])
The string STRING is repeatedly compared against a series of REGEX
arguments; if a match is found, the expansion is the corresponding
VALUE, otherwise, the macro moves on to the next REGEX. If no
REGEX match, then the result is the optional DEFAULT, or nothing.
-- Macro: m4_bpatsubsts (STRING, REGEX-1, SUBST-1, [REGEX-2],
[SUBST-2], ...)
The string STRING is altered by REGEX-1 and SUBST-1, as if by:
m4_bpatsubst([[STRING]], [REGEX], [SUBST])
The result of the substitution is then passed through the next set
of REGEX and SUBST, and so forth. An empty SUBST implies deletion
of any matched portions in the current string. Note that this
macro over-quotes STRING; this behavior is intentional, so that
the result of each step of the recursion remains as a quoted
string. However, it means that anchors (`^' and `$' in the REGEX
will line up with the extra quotations, and not the characters of
the original string. The overquoting is removed after the final
substitution.
-- Macro: m4_case (STRING, VALUE-1, IF-VALUE-1, [VALUE-2],
[IF-VALUE-2], ..., [DEFAULT])
Test STRING against multiple VALUE possibilities, resulting in the
first IF-VALUE for a match, or in the optional DEFAULT. This is
shorthand for:
m4_if([STRING], [VALUE-1], [IF-VALUE-1],
[STRING], [VALUE-2], [IF-VALUE-2], ...,
[DEFAULT])
-- Macro: m4_cond (TEST-1, VALUE-1, IF-VALUE-1, [TEST-2], [VALUE-2],
[IF-VALUE-2], ..., [DEFAULT])
This macro was introduced in Autoconf 2.62. Similar to `m4_if',
except that each TEST is expanded only when it is encountered.
This is useful for short-circuiting expensive tests; while `m4_if'
requires all its strings to be expanded up front before doing
comparisons, `m4_cond' only expands a TEST when all earlier tests
have failed.
For an example, these two sequences give the same result, but in
the case where `$1' does not contain a backslash, the `m4_cond'
version only expands `m4_index' once, instead of five times, for
faster computation if this is a common case for `$1'. Notice that
every third argument is unquoted for `m4_if', and quoted for
`m4_cond':
m4_if(m4_index([$1], [\]), [-1], [$2],
m4_eval(m4_index([$1], [\\]) >= 0), [1], [$2],
m4_eval(m4_index([$1], [\$]) >= 0), [1], [$2],
m4_eval(m4_index([$1], [\`]) >= 0), [1], [$3],
m4_eval(m4_index([$1], [\"]) >= 0), [1], [$3],
[$2])
m4_cond([m4_index([$1], [\])], [-1], [$2],
[m4_eval(m4_index([$1], [\\]) >= 0)], [1], [$2],
[m4_eval(m4_index([$1], [\$]) >= 0)], [1], [$2],
[m4_eval(m4_index([$1], [\`]) >= 0)], [1], [$3],
[m4_eval(m4_index([$1], [\"]) >= 0)], [1], [$3],
[$2])
-- Macro: m4_default (EXPR-1, EXPR-2)
-- Macro: m4_default_quoted (EXPR-1, EXPR-2)
-- Macro: m4_default_nblank (EXPR-1, [EXPR-2])
-- Macro: m4_default_nblank_quoted (EXPR-1, [EXPR-2])
If EXPR-1 contains text, use it. Otherwise, select EXPR-2.
`m4_default' expands the result, while `m4_default_quoted' does
not. Useful for providing a fixed default if the expression that
results in EXPR-1 would otherwise be empty. The difference
between `m4_default' and `m4_default_nblank' is whether an
argument consisting of just blanks (space, tab, newline) is
significant. When using the expanding versions, note that an
argument may contain text but still expand to an empty string.
m4_define([active], [ACTIVE])dnl
m4_define([empty], [])dnl
m4_define([demo1], [m4_default([$1], [$2])])dnl
m4_define([demo2], [m4_default_quoted([$1], [$2])])dnl
m4_define([demo3], [m4_default_nblank([$1], [$2])])dnl
m4_define([demo4], [m4_default_nblank_quoted([$1], [$2])])dnl
demo1([active], [default])
=>ACTIVE
demo1([], [active])
=>ACTIVE
demo1([empty], [text])
=>
-demo1([ ], [active])-
=>- -
demo2([active], [default])
=>active
demo2([], [active])
=>active
demo2([empty], [text])
=>empty
-demo2([ ], [active])-
=>- -
demo3([active], [default])
=>ACTIVE
demo3([], [active])
=>ACTIVE
demo3([empty], [text])
=>
-demo3([ ], [active])-
=>-ACTIVE-
demo4([active], [default])
=>active
demo4([], [active])
=>active
demo4([empty], [text])
=>empty
-demo4([ ], [active])-
=>-active-
-- Macro: m4_define_default (MACRO, [DEFAULT-DEFINITION])
If MACRO does not already have a definition, then define it to
DEFAULT-DEFINITION.
-- Macro: m4_ifblank (COND, [IF-BLANK], [IF-TEXT])
-- Macro: m4_ifnblank (COND, [IF-TEXT], [IF-BLANK])
If COND is empty or consists only of blanks (space, tab, newline),
then expand IF-BLANK; otherwise, expand IF-TEXT. Two variants
exist, in order to make it easier to select the correct logical
sense when using only two parameters. Note that this is more
efficient than the equivalent behavior of:
m4_ifval(m4_normalize([COND]), IF-TEXT, IF-BLANK)
-- Macro: m4_ifndef (MACRO, IF-NOT-DEFINED, [IF-DEFINED])
This is shorthand for:
m4_ifdef([MACRO], [IF-DEFINED], [IF-NOT-DEFINED])
-- Macro: m4_ifset (MACRO, [IF-TRUE], [IF-FALSE])
If MACRO is undefined, or is defined as the empty string, expand
to IF-FALSE. Otherwise, expands to IF-TRUE. Similar to:
m4_ifval(m4_defn([MACRO]), [IF-TRUE], [IF-FALSE])
except that it is not an error if MACRO is undefined.
-- Macro: m4_ifval (COND, [IF-TRUE], [IF-FALSE])
Expands to IF-TRUE if COND is not empty, otherwise to IF-FALSE.
This is shorthand for:
m4_if([COND], [], [IF-FALSE], [IF-TRUE])
-- Macro: m4_ifvaln (COND, [IF-TRUE], [IF-FALSE])
Similar to `m4_ifval', except guarantee that a newline is present
after any non-empty expansion. Often followed by `dnl'.
-- Macro: m4_n (TEXT)
Expand to TEXT, and add a newline if TEXT is not empty. Often
followed by `dnl'.
File: autoconf.info, Node: Looping constructs, Next: Evaluation Macros, Prev: Conditional constructs, Up: Programming in M4sugar
8.3.5 Looping constructs
------------------------
The following macros are useful in implementing recursive algorithms in
M4, including loop operations. An M4 list is formed by quoting a list
of quoted elements; generally the lists are comma-separated, although
`m4_foreach_w' is whitespace-separated. For example, the list `[[a],
[b,c]]' contains two elements: `[a]' and `[b,c]'. It is common to see
lists with unquoted elements when those elements are not likely to be
macro names, as in `[fputc_unlocked, fgetc_unlocked]'.
Although not generally recommended, it is possible for quoted lists
to have side effects; all side effects are expanded only once, and
prior to visiting any list element. On the other hand, the fact that
unquoted macros are expanded exactly once means that macros without
side effects can be used to generate lists. For example,
m4_foreach([i], [[1], [2], [3]m4_errprintn([hi])], [i])
error-->hi
=>123
m4_define([list], [[1], [2], [3]])
=>
m4_foreach([i], [list], [i])
=>123
-- Macro: m4_argn (N, [ARG]...)
Extracts argument N (larger than 0) from the remaining arguments.
If there are too few arguments, the empty string is used. For any
N besides 1, this is more efficient than the similar
`m4_car(m4_shiftn([N], [], [ARG...]))'.
-- Macro: m4_car (ARG...)
Expands to the quoted first ARG. Can be used with `m4_cdr' to
recursively iterate through a list. Generally, when using quoted
lists of quoted elements, `m4_car' should be called without any
extra quotes.
-- Macro: m4_cdr (ARG...)
Expands to a quoted list of all but the first ARG, or the empty
string if there was only one argument. Generally, when using
quoted lists of quoted elements, `m4_cdr' should be called without
any extra quotes.
For example, this is a simple implementation of `m4_map'; note how
each iteration checks for the end of recursion, then merely
applies the first argument to the first element of the list, then
repeats with the rest of the list. (The actual implementation in
M4sugar is a bit more involved, to gain some speed and share code
with `m4_map_sep', and also to avoid expanding side effects in
`$2' twice).
m4_define([m4_map], [m4_ifval([$2],
[m4_apply([$1], m4_car($2))[]$0([$1], m4_cdr($2))])])dnl
m4_map([ m4_eval], [[[1]], [[1+1]], [[10],[16]]])
=> 1 2 a
-- Macro: m4_for (VAR, FIRST, LAST, [STEP], EXPRESSION)
Loop over the numeric values between FIRST and LAST including
bounds by increments of STEP. For each iteration, expand
EXPRESSION with the numeric value assigned to VAR. If STEP is
omitted, it defaults to `1' or `-1' depending on the order of the
limits. If given, STEP has to match this order. The number of
iterations is determined independently from definition of VAR;
iteration cannot be short-circuited or lengthened by modifying VAR
from within EXPRESSION.
-- Macro: m4_foreach (VAR, LIST, EXPRESSION)
Loop over the comma-separated M4 list LIST, assigning each value
to VAR, and expand EXPRESSION. The following example outputs two
lines:
m4_foreach([myvar], [[foo], [bar, baz]],
[echo myvar
])dnl
=>echo foo
=>echo bar, baz
Note that for some forms of EXPRESSION, it may be faster to use
`m4_map_args'.
-- Macro: m4_foreach_w (VAR, LIST, EXPRESSION)
Loop over the white-space-separated list LIST, assigning each value
to VAR, and expand EXPRESSION. If VAR is only referenced once in
EXPRESSION, it is more efficient to use `m4_map_args_w'.
The deprecated macro `AC_FOREACH' is an alias of `m4_foreach_w'.
-- Macro: m4_map (MACRO, LIST)
-- Macro: m4_mapall (MACRO, LIST)
-- Macro: m4_map_sep (MACRO, SEPARATOR, LIST)
-- Macro: m4_mapall_sep (MACRO, SEPARATOR, LIST)
Loop over the comma separated quoted list of argument descriptions
in LIST, and invoke MACRO with the arguments. An argument
description is in turn a comma-separated quoted list of quoted
elements, suitable for `m4_apply'. The macros `m4_map' and
`m4_map_sep' ignore empty argument descriptions, while `m4_mapall'
and `m4_mapall_sep' invoke MACRO with no arguments. The macros
`m4_map_sep' and `m4_mapall_sep' additionally expand SEPARATOR
between invocations of MACRO.
Note that SEPARATOR is expanded, unlike in `m4_join'. When
separating output with commas, this means that the map result can
be used as a series of arguments, by using a single-quoted comma as
SEPARATOR, or as a single string, by using a double-quoted comma.
m4_map([m4_count], [])
=>
m4_map([ m4_count], [[],
[[1]],
[[1], [2]]])
=> 1 2
m4_mapall([ m4_count], [[],
[[1]],
[[1], [2]]])
=> 0 1 2
m4_map_sep([m4_eval], [,], [[[1+2]],
[[10], [16]]])
=>3,a
m4_map_sep([m4_echo], [,], [[[a]], [[b]]])
=>a,b
m4_count(m4_map_sep([m4_echo], [,], [[[a]], [[b]]]))
=>2
m4_map_sep([m4_echo], [[,]], [[[a]], [[b]]])
=>a,b
m4_count(m4_map_sep([m4_echo], [[,]], [[[a]], [[b]]]))
=>1
-- Macro: m4_map_args (MACRO, ARG...)
Repeatedly invoke MACRO with each successive ARG as its only
argument. In the following example, three solutions are presented
with the same expansion; the solution using `m4_map_args' is the
most efficient.
m4_define([active], [ACTIVE])dnl
m4_foreach([var], [[plain], [active]], [ m4_echo(m4_defn([var]))])
=> plain active
m4_map([ m4_echo], [[[plain]], [[active]]])
=> plain active
m4_map_args([ m4_echo], [plain], [active])
=> plain active
In cases where it is useful to operate on additional parameters
besides the list elements, the macro `m4_curry' can be used in
MACRO to supply the argument currying necessary to generate the
desired argument list. In the following example, `list_add_n' is
more efficient than `list_add_x'. On the other hand, using
`m4_map_args_sep' can be even more efficient.
m4_define([list], [[1], [2], [3]])dnl
m4_define([add], [m4_eval(([$1]) + ([$2]))])dnl
dnl list_add_n(N, ARG...)
dnl Output a list consisting of each ARG added to N
m4_define([list_add_n],
[m4_shift(m4_map_args([,m4_curry([add], [$1])], m4_shift($@)))])dnl
list_add_n([1], list)
=>2,3,4
list_add_n([2], list)
=>3,4,5
m4_define([list_add_x],
[m4_shift(m4_foreach([var], m4_dquote(m4_shift($@)),
[,add([$1],m4_defn([var]))]))])dnl
list_add_x([1], list)
=>2,3,4
-- Macro: m4_map_args_pair (MACRO, [MACRO-END = `macro'], ARG...)
For every pair of arguments ARG, invoke MACRO with two arguments.
If there is an odd number of arguments, invoke MACRO-END, which
defaults to MACRO, with the remaining argument.
m4_map_args_pair([, m4_reverse], [], [1], [2], [3])
=>, 2, 1, 3
m4_map_args_pair([, m4_reverse], [, m4_dquote], [1], [2], [3])
=>, 2, 1, [3]
m4_map_args_pair([, m4_reverse], [, m4_dquote], [1], [2], [3], [4])
=>, 2, 1, 4, 3
-- Macro: m4_map_args_sep ([PRE], [POST], [SEP], ARG...)
Expand the sequence `PRE[ARG]POST' for each argument, additionally
expanding SEP between arguments. One common use of this macro is
constructing a macro call, where the opening and closing
parentheses are split between PRE and POST; in particular,
`m4_map_args([MACRO], [ARG])' is equivalent to
`m4_map_args_sep([MACRO(], [)], [], [ARG])'. This macro provides
the most efficient means for iterating over an arbitrary list of
arguments, particularly when repeatedly constructing a macro call
with more arguments than ARG.
-- Macro: m4_map_args_w (STRING, [PRE], [POST], [SEP])
Expand the sequence `PRE[word]POST' for each word in the
whitespace-separated STRING, additionally expanding SEP between
words. This macro provides the most efficient means for iterating
over a whitespace-separated string. In particular,
`m4_map_args_w([STRING], [ACTION(], [)])' is more efficient than
`m4_foreach_w([var], [STRING], [ACTION(m4_defn([var]))])'.
-- Macro: m4_shiftn (COUNT, ...)
-- Macro: m4_shift2 (...)
-- Macro: m4_shift3 (...)
`m4_shiftn' performs COUNT iterations of `m4_shift', along with
validation that enough arguments were passed in to match the shift
count, and that the count is positive. `m4_shift2' and
`m4_shift3' are specializations of `m4_shiftn', introduced in
Autoconf 2.62, and are more efficient for two and three shifts,
respectively.
-- Macro: m4_stack_foreach (MACRO, ACTION)
-- Macro: m4_stack_foreach_lifo (MACRO, ACTION)
For each of the `m4_pushdef' definitions of MACRO, expand ACTION
with the single argument of a definition of MACRO.
`m4_stack_foreach' starts with the oldest definition, while
`m4_stack_foreach_lifo' starts with the current definition.
ACTION should not push or pop definitions of MACRO, nor is there
any guarantee that the current definition of MACRO matches the
argument that was passed to ACTION. The macro `m4_curry' can be
used if ACTION needs more than one argument, although in that case
it is more efficient to use M4_STACK_FOREACH_SEP.
Due to technical limitations, there are a few low-level m4sugar
functions, such as `m4_pushdef', that cannot be used as the MACRO
argument.
m4_pushdef([a], [1])m4_pushdef([a], [2])dnl
m4_stack_foreach([a], [ m4_incr])
=> 2 3
m4_stack_foreach_lifo([a], [ m4_curry([m4_substr], [abcd])])
=> cd bcd
-- Macro: m4_stack_foreach_sep (MACRO, [PRE], [POST], [SEP])
-- Macro: m4_stack_foreach_sep_lifo (MACRO, [PRE], [POST], [SEP])
Expand the sequence `PRE[definition]POST' for each `m4_pushdef'
definition of MACRO, additionally expanding SEP between
definitions. `m4_stack_foreach_sep' visits the oldest definition
first, while `m4_stack_foreach_sep_lifo' visits the current
definition first. This macro provides the most efficient means
for iterating over a pushdef stack. In particular,
`m4_stack_foreach([MACRO], [ACTION])' is short for
`m4_stack_foreach_sep([MACRO], [ACTION(], [)])'.
File: autoconf.info, Node: Evaluation Macros, Next: Text processing Macros, Prev: Looping constructs, Up: Programming in M4sugar
8.3.6 Evaluation Macros
-----------------------
The following macros give some control over the order of the evaluation
by adding or removing levels of quotes.
-- Macro: m4_apply (MACRO, LIST)
Apply the elements of the quoted, comma-separated LIST as the
arguments to MACRO. If LIST is empty, invoke MACRO without
arguments. Note the difference between `m4_indir', which expects
its first argument to be a macro name but can use names that are
otherwise invalid, and `m4_apply', where MACRO can contain other
text, but must end in a valid macro name.
m4_apply([m4_count], [])
=>0
m4_apply([m4_count], [[]])
=>1
m4_apply([m4_count], [[1], [2]])
=>2
m4_apply([m4_join], [[|], [1], [2]])
=>1|2
-- Macro: m4_count (ARG, ...)
This macro returns the decimal count of the number of arguments it
was passed.
-- Macro: m4_curry (MACRO, ARG...)
This macro performs argument currying. The expansion of this
macro is another macro name that expects exactly one argument;
that argument is then appended to the ARG list, and then MACRO is
expanded with the resulting argument list.
m4_curry([m4_curry], [m4_reverse], [1])([2])([3])
=>3, 2, 1
Unfortunately, due to a limitation in M4 1.4.x, it is not possible
to pass the definition of a builtin macro as the argument to the
output of `m4_curry'; the empty string is used instead of the
builtin token. This behavior is rectified by using M4 1.6 or
newer.
-- Macro: m4_do (ARG, ...)
This macro loops over its arguments and expands each ARG in
sequence. Its main use is for readability; it allows the use of
indentation and fewer `dnl' to result in the same expansion. This
macro guarantees that no expansion will be concatenated with
subsequent text; to achieve full concatenation, use
`m4_unquote(m4_join([], ARG...))'.
m4_define([ab],[1])m4_define([bc],[2])m4_define([abc],[3])dnl
m4_do([a],[b])c
=>abc
m4_unquote(m4_join([],[a],[b]))c
=>3
m4_define([a],[A])m4_define([b],[B])m4_define([c],[C])dnl
m4_define([AB],[4])m4_define([BC],[5])m4_define([ABC],[6])dnl
m4_do([a],[b])c
=>ABC
m4_unquote(m4_join([],[a],[b]))c
=>3
-- Macro: m4_dquote (ARG, ...)
Return the arguments as a quoted list of quoted arguments.
Conveniently, if there is just one ARG, this effectively adds a
level of quoting.
-- Macro: m4_dquote_elt (ARG, ...)
Return the arguments as a series of double-quoted arguments.
Whereas `m4_dquote' returns a single argument, `m4_dquote_elt'
returns as many arguments as it was passed.
-- Macro: m4_echo (ARG, ...)
Return the arguments, with the same level of quoting. Other than
discarding whitespace after unquoted commas, this macro is a no-op.
-- Macro: m4_expand (ARG)
Return the expansion of ARG as a quoted string. Whereas
`m4_quote' is designed to collect expanded text into a single
argument, `m4_expand' is designed to perform one level of expansion
on quoted text. One distinction is in the treatment of whitespace
following a comma in the original ARG. Any time multiple
arguments are collected into one with `m4_quote', the M4 argument
collection rules discard the whitespace. However, with
`m4_expand', whitespace is preserved, even after the expansion of
macros contained in ARG. Additionally, `m4_expand' is able to
expand text that would involve an unterminated comment, whereas
expanding that same text as the argument to `m4_quote' runs into
difficulty in finding the end of the argument. Since manipulating
diversions during argument collection is inherently unsafe,
`m4_expand' issues an error if ARG attempts to change the current
diversion (*note Diversion support::).
m4_define([active], [ACT, IVE])dnl
m4_define([active2], [[ACT, IVE]])dnl
m4_quote(active, active)
=>ACT,IVE,ACT,IVE
m4_expand([active, active])
=>ACT, IVE, ACT, IVE
m4_quote(active2, active2)
=>ACT, IVE,ACT, IVE
m4_expand([active2, active2])
=>ACT, IVE, ACT, IVE
m4_expand([# m4_echo])
=># m4_echo
m4_quote(# m4_echo)
)
=># m4_echo)
=>
Note that `m4_expand' cannot handle an ARG that expands to literal
unbalanced quotes, but that quadrigraphs can be used when
unbalanced output is necessary. Likewise, unbalanced parentheses
should be supplied with double quoting or a quadrigraph.
m4_define([pattern], [[!@case $foo in
=> [![]) BAR ;;
=> *) blah ;;
=>esac
-- Macro: m4_ignore (...)
This macro was introduced in Autoconf 2.62. Expands to nothing,
ignoring all of its arguments. By itself, this isn't very useful.
However, it can be used to conditionally ignore an arbitrary
number of arguments, by deciding which macro name to apply to a
list of arguments.
dnl foo outputs a message only if [debug] is defined.
m4_define([foo],
[m4_ifdef([debug],[AC_MSG_NOTICE],[m4_ignore])([debug message])])
Note that for earlier versions of Autoconf, the macro `__gnu__' can
serve the same purpose, although it is less readable.
-- Macro: m4_make_list (ARG, ...)
This macro exists to aid debugging of M4sugar algorithms. Its net
effect is similar to `m4_dquote'--it produces a quoted list of
quoted arguments, for each ARG. The difference is that this
version uses a comma-newline separator instead of just comma, to
improve readability of the list; with the result that it is less
efficient than `m4_dquote'.
m4_define([zero],[0])m4_define([one],[1])m4_define([two],[2])dnl
m4_dquote(zero, [one], [[two]])
=>[0],[one],[[two]]
m4_make_list(zero, [one], [[two]])
=>[0],
=>[one],
=>[[two]]
m4_foreach([number], m4_dquote(zero, [one], [[two]]), [ number])
=> 0 1 two
m4_foreach([number], m4_make_list(zero, [one], [[two]]), [ number])
=> 0 1 two
-- Macro: m4_quote (ARG, ...)
Return the arguments as a single entity, i.e., wrap them into a
pair of quotes. This effectively collapses multiple arguments
into one, although it loses whitespace after unquoted commas in
the process.
-- Macro: m4_reverse (ARG, ...)
Outputs each argument with the same level of quoting, but in
reverse order, and with space following each comma for readability.
m4_define([active], [ACT,IVE])
=>
m4_reverse(active, [active])
=>active, IVE, ACT
-- Macro: m4_unquote (ARG, ...)
This macro was introduced in Autoconf 2.62. Expand each argument,
separated by commas. For a single ARG, this effectively removes a
layer of quoting, and `m4_unquote([ARG])' is more efficient than
the equivalent `m4_do([ARG])'. For multiple arguments, this
results in an unquoted list of expansions. This is commonly used
with `m4_split', in order to convert a single quoted list into a
series of quoted elements.
The following example aims at emphasizing the difference between
several scenarios: not using these macros, using `m4_defn', using
`m4_quote', using `m4_dquote', and using `m4_expand'.
$ cat example.m4
dnl Overquote, so that quotes are visible.
m4_define([show], [$[]1 = [$1], $[]@ = [$@]])
m4_define([a], [A])
m4_define([mkargs], [1, 2[,] 3])
m4_define([arg1], [[$1]])
m4_divert([0])dnl
show(a, b)
show([a, b])
show(m4_quote(a, b))
show(m4_dquote(a, b))
show(m4_expand([a, b]))
arg1(mkargs)
arg1([mkargs])
arg1(m4_defn([mkargs]))
arg1(m4_quote(mkargs))
arg1(m4_dquote(mkargs))
arg1(m4_expand([mkargs]))
$ autom4te -l m4sugar example.m4
$1 = A, $@ = [A],[b]
$1 = a, b, $@ = [a, b]
$1 = A,b, $@ = [A,b]
$1 = [A],[b], $@ = [[A],[b]]
$1 = A, b, $@ = [A, b]
1
mkargs
1, 2[,] 3
1,2, 3
[1],[2, 3]
1, 2, 3
File: autoconf.info, Node: Text processing Macros, Next: Number processing Macros, Prev: Evaluation Macros, Up: Programming in M4sugar
8.3.7 String manipulation in M4
-------------------------------
The following macros may be used to manipulate strings in M4. Many of
the macros in this section intentionally result in quoted strings as
output, rather than subjecting the arguments to further expansions. As
a result, if you are manipulating text that contains active M4
characters, the arguments are passed with single quoting rather than
double.
-- Macro: m4_append (MACRO-NAME, STRING, [SEPARATOR])
-- Macro: m4_append_uniq (MACRO-NAME, STRING, [SEPARATOR] [IF-UNIQ],
[IF-DUPLICATE])
Redefine MACRO-NAME to its former contents with SEPARATOR and
STRING added at the end. If MACRO-NAME was undefined before (but
not if it was defined but empty), then no SEPARATOR is added. As
of Autoconf 2.62, neither STRING nor SEPARATOR are expanded during
this macro; instead, they are expanded when MACRO-NAME is invoked.
`m4_append' can be used to grow strings, and `m4_append_uniq' to
grow strings without duplicating substrings. Additionally,
`m4_append_uniq' takes two optional parameters as of Autoconf 2.62;
IF-UNIQ is expanded if STRING was appended, and IF-DUPLICATE is
expanded if STRING was already present. Also, `m4_append_uniq'
warns if SEPARATOR is not empty, but occurs within STRING, since
that can lead to duplicates.
Note that `m4_append' can scale linearly in the length of the final
string, depending on the quality of the underlying M4
implementation, while `m4_append_uniq' has an inherent quadratic
scaling factor. If an algorithm can tolerate duplicates in the
final string, use the former for speed. If duplicates must be
avoided, consider using `m4_set_add' instead (*note Set
manipulation Macros::).
m4_define([active], [ACTIVE])dnl
m4_append([sentence], [This is an])dnl
m4_append([sentence], [ active ])dnl
m4_append([sentence], [symbol.])dnl
sentence
=>This is an ACTIVE symbol.
m4_undefine([active])dnl
=>This is an active symbol.
m4_append_uniq([list], [one], [, ], [new], [existing])
=>new
m4_append_uniq([list], [one], [, ], [new], [existing])
=>existing
m4_append_uniq([list], [two], [, ], [new], [existing])
=>new
m4_append_uniq([list], [three], [, ], [new], [existing])
=>new
m4_append_uniq([list], [two], [, ], [new], [existing])
=>existing
list
=>one, two, three
m4_dquote(list)
=>[one],[two],[three]
m4_append([list2], [one], [[, ]])dnl
m4_append_uniq([list2], [two], [[, ]])dnl
m4_append([list2], [three], [[, ]])dnl
list2
=>one, two, three
m4_dquote(list2)
=>[one, two, three]
-- Macro: m4_append_uniq_w (MACRO-NAME, STRINGS)
This macro was introduced in Autoconf 2.62. It is similar to
`m4_append_uniq', but treats STRINGS as a whitespace separated
list of words to append, and only appends unique words.
MACRO-NAME is updated with a single space between new words.
m4_append_uniq_w([numbers], [1 1 2])dnl
m4_append_uniq_w([numbers], [ 2 3 ])dnl
numbers
=>1 2 3
-- Macro: m4_chomp (STRING)
-- Macro: m4_chomp_all (STRING)
Output STRING in quotes, but without a trailing newline. The
macro `m4_chomp' is slightly faster, and removes at most one
newline; the macro `m4_chomp_all' removes all consecutive trailing
newlines. Unlike `m4_flatten', embedded newlines are left intact,
and backslash does not influence the result.
-- Macro: m4_combine ([SEPARATOR], PREFIX-LIST, [INFIX], SUFFIX-1,
[SUFFIX-2], ...)
This macro produces a quoted string containing the pairwise
combination of every element of the quoted, comma-separated
PREFIX-LIST, and every element from the SUFFIX arguments. Each
pairwise combination is joined with INFIX in the middle, and
successive pairs are joined by SEPARATOR. No expansion occurs on
any of the arguments. No output occurs if either the PREFIX or
SUFFIX list is empty, but the lists can contain empty elements.
m4_define([a], [oops])dnl
m4_combine([, ], [[a], [b], [c]], [-], [1], [2], [3])
=>a-1, a-2, a-3, b-1, b-2, b-3, c-1, c-2, c-3
m4_combine([, ], [[a], [b]], [-])
=>
m4_combine([, ], [[a], [b]], [-], [])
=>a-, b-
m4_combine([, ], [], [-], [1], [2])
=>
m4_combine([, ], [[]], [-], [1], [2])
=>-1, -2
-- Macro: m4_escape (STRING)
Convert all instances of `[', `]', `#', and `$' within STRING into
their respective quadrigraphs. The result is still a quoted
string.
-- Macro: m4_flatten (STRING)
Flatten STRING into a single line. Delete all backslash-newline
pairs, and replace all remaining newlines with a space. The
result is still a quoted string.
-- Macro: m4_join ([SEPARATOR], ARGS...)
-- Macro: m4_joinall ([SEPARATOR], ARGS...)
Concatenate each ARG, separated by SEPARATOR. `joinall' uses
every argument, while `join' omits empty arguments so that there
are no back-to-back separators in the output. The result is a
quoted string.
m4_define([active], [ACTIVE])dnl
m4_join([|], [one], [], [active], [two])
=>one|active|two
m4_joinall([|], [one], [], [active], [two])
=>one||active|two
Note that if all you intend to do is join ARGS with commas between
them, to form a quoted list suitable for `m4_foreach', it is more
efficient to use `m4_dquote'.
-- Macro: m4_newline ([TEXT])
This macro was introduced in Autoconf 2.62, and expands to a
newline, followed by any TEXT. It is primarily useful for
maintaining macro formatting, and ensuring that M4 does not
discard leading whitespace during argument collection.
-- Macro: m4_normalize (STRING)
Remove leading and trailing spaces and tabs, sequences of
backslash-then-newline, and replace multiple spaces, tabs, and
newlines with a single space. This is a combination of
`m4_flatten' and `m4_strip'. To determine if STRING consists only
of bytes that would be removed by `m4_normalize', you can use
`m4_ifblank'.
-- Macro: m4_re_escape (STRING)
Backslash-escape all characters in STRING that are active in
regexps.
-- Macro: m4_split (STRING, [REGEXP = `[\t ]+'])
Split STRING into an M4 list of elements quoted by `[' and `]',
while keeping white space at the beginning and at the end. If
REGEXP is given, use it instead of `[\t ]+' for splitting. If
STRING is empty, the result is an empty list.
-- Macro: m4_strip (STRING)
Strip whitespace from STRING. Sequences of spaces and tabs are
reduced to a single space, then leading and trailing spaces are
removed. The result is still a quoted string. Note that this
does not interfere with newlines; if you want newlines stripped as
well, consider `m4_flatten', or do it all at once with
`m4_normalize'. To quickly test if STRING has only whitespace,
use `m4_ifblank'.
-- Macro: m4_text_box (MESSAGE, [FRAME = `-'])
Add a text box around MESSAGE, using FRAME as the border character
above and below the message. The FRAME argument must be a single
byte, and does not support quadrigraphs. The frame correctly
accounts for the subsequent expansion of MESSAGE. For example:
m4_define([macro], [abc])dnl
m4_text_box([macro])
=>## --- ##
=>## abc ##
=>## --- ##
The MESSAGE must contain balanced quotes and parentheses, although
quadrigraphs can be used to work around this.
-- Macro: m4_text_wrap (STRING, [PREFIX], [PREFIX1 = `PREFIX'], [WIDTH
= `79'])
Break STRING into a series of whitespace-separated words, then
output those words separated by spaces, and wrapping lines any
time the output would exceed WIDTH columns. If given, PREFIX1
begins the first line, and PREFIX begins all wrapped lines. If
PREFIX1 is longer than PREFIX, then the first line consists of
just PREFIX1. If PREFIX is longer than PREFIX1, padding is
inserted so that the first word of STRING begins at the same
indentation as all wrapped lines. Note that using literal tab
characters in any of the arguments will interfere with the
calculation of width. No expansions occur on PREFIX, PREFIX1, or
the words of STRING, although quadrigraphs are recognized.
For some examples:
m4_text_wrap([Short string */], [ ], [/* ], [20])
=>/* Short string */
m4_text_wrap([Much longer string */], [ ], [/* ], [20])
=>/* Much longer
=> string */
m4_text_wrap([Short doc.], [ ], [ --short ], [30])
=> --short Short doc.
m4_text_wrap([Short doc.], [ ], [ --too-wide ], [30])
=> --too-wide
=> Short doc.
m4_text_wrap([Super long documentation.], [ ],
[ --too-wide ], 30)
=> --too-wide
=> Super long
=> documentation.
-- Macro: m4_tolower (STRING)
-- Macro: m4_toupper (STRING)
Return STRING with letters converted to upper or lower case,
respectively.
File: autoconf.info, Node: Number processing Macros, Next: Set manipulation Macros, Prev: Text processing Macros, Up: Programming in M4sugar
8.3.8 Arithmetic computation in M4
----------------------------------
The following macros facilitate integer arithmetic operations. Where a
parameter is documented as taking an arithmetic expression, you can use
anything that can be parsed by `m4_eval'.
-- Macro: m4_cmp (EXPR-1, EXPR-2)
Compare the arithmetic expressions EXPR-1 and EXPR-2, and expand
to `-1' if EXPR-1 is smaller, `0' if they are equal, and `1' if
EXPR-1 is larger.
-- Macro: m4_list_cmp (LIST-1, LIST-2)
Compare the two M4 lists consisting of comma-separated arithmetic
expressions, left to right. Expand to `-1' for the first element
pairing where the value from LIST-1 is smaller, `1' where the
value from LIST-2 is smaller, or `0' if both lists have the same
values. If one list is shorter than the other, the remaining
elements of the longer list are compared against zero.
m4_list_cmp([1, 0], [1])
=>0
m4_list_cmp([1, [1 * 0]], [1, 0])
=>0
m4_list_cmp([1, 2], [1, 0])
=>1
m4_list_cmp([1, [1+1], 3],[1, 2])
=>1
m4_list_cmp([1, 2, -3], [1, 2])
=>-1
m4_list_cmp([1, 0], [1, 2])
=>-1
m4_list_cmp([1], [1, 2])
=>-1
-- Macro: m4_max (ARG, ...)
This macro was introduced in Autoconf 2.62. Expand to the decimal
value of the maximum arithmetic expression among all the arguments.
-- Macro: m4_min (ARG, ...)
This macro was introduced in Autoconf 2.62. Expand to the decimal
value of the minimum arithmetic expression among all the arguments.
-- Macro: m4_sign (EXPR)
Expand to `-1' if the arithmetic expression EXPR is negative, `1'
if it is positive, and `0' if it is zero.
-- Macro: m4_version_compare (VERSION-1, VERSION-2)
This macro was introduced in Autoconf 2.53, but had a number of
usability limitations that were not lifted until Autoconf 2.62.
Compare the version strings VERSION-1 and VERSION-2, and expand to
`-1' if VERSION-1 is smaller, `0' if they are the same, or `1'
VERSION-2 is smaller. Version strings must be a list of elements
separated by `.', `,' or `-', where each element is a number along
with optional case-insensitive letters designating beta releases.
The comparison stops at the leftmost element that contains a
difference, although a 0 element compares equal to a missing
element.
It is permissible to include commit identifiers in VERSION, such
as an abbreviated SHA1 of the commit, provided there is still a
monotonically increasing prefix to allow for accurate version-based
comparisons. For example, this paragraph was written when the
development snapshot of autoconf claimed to be at version
`2.61a-248-dc51', or 248 commits after the 2.61a release, with an
abbreviated commit identification of `dc51'.
m4_version_compare([1.1], [2.0])
=>-1
m4_version_compare([2.0b], [2.0a])
=>1
m4_version_compare([1.1.1], [1.1.1a])
=>-1
m4_version_compare([1.2], [1.1.1a])
=>1
m4_version_compare([1.0], [1])
=>0
m4_version_compare([1.1pre], [1.1PRE])
=>0
m4_version_compare([1.1a], [1,10])
=>-1
m4_version_compare([2.61a], [2.61a-248-dc51])
=>-1
m4_version_compare([2.61b], [2.61a-248-dc51])
=>1
-- Macro: m4_version_prereq (VERSION, [IF-NEW-ENOUGH], [IF-OLD =
`m4_fatal'])
Compares VERSION against the version of Autoconf currently
running. If the running version is at VERSION or newer, expand
IF-NEW-ENOUGH, but if VERSION is larger than the version currently
executing, expand IF-OLD, which defaults to printing an error
message and exiting m4sugar with status 63. When given only one
argument, this behaves like `AC_PREREQ' (*note Versioning::).
Remember that the autoconf philosophy favors feature checks over
version checks.
File: autoconf.info, Node: Set manipulation Macros, Next: Forbidden Patterns, Prev: Number processing Macros, Up: Programming in M4sugar
8.3.9 Set manipulation in M4
----------------------------
Sometimes, it is necessary to track a set of data, where the order does
not matter and where there are no duplicates in the set. The following
macros facilitate set manipulations. Each set is an opaque object,
which can only be accessed via these basic operations. The underlying
implementation guarantees linear scaling for set creation, which is more
efficient than using the quadratic `m4_append_uniq'. Both set names
and values can be arbitrary strings, except for unbalanced quotes.
This implementation ties up memory for removed elements until the next
operation that must traverse all the elements of a set; and although
that may slow down some operations until the memory for removed elements
is pruned, it still guarantees linear performance.
-- Macro: m4_set_add (SET, VALUE, [IF-UNIQ], [IF-DUP])
Adds the string VALUE as a member of set SET. Expand IF-UNIQ if
the element was added, or IF-DUP if it was previously in the set.
Operates in amortized constant time, so that set creation scales
linearly.
-- Macro: m4_set_add_all (SET, VALUE...)
Adds each VALUE to the set SET. This is slightly more efficient
than repeatedly invoking `m4_set_add'.
-- Macro: m4_set_contains (SET, VALUE, [IF-PRESENT], [IF-ABSENT])
Expands IF-PRESENT if the string VALUE is a member of SET,
otherwise IF-ABSENT.
m4_set_contains([a], [1], [yes], [no])
=>no
m4_set_add([a], [1], [added], [dup])
=>added
m4_set_add([a], [1], [added], [dup])
=>dup
m4_set_contains([a], [1], [yes], [no])
=>yes
m4_set_remove([a], [1], [removed], [missing])
=>removed
m4_set_contains([a], [1], [yes], [no])
=>no
m4_set_remove([a], [1], [removed], [missing])
=>missing
-- Macro: m4_set_contents (SET, [SEP])
-- Macro: m4_set_dump (SET, [SEP])
Expands to a single string consisting of all the members of the set
SET, each separated by SEP, which is not expanded.
`m4_set_contents' leaves the elements in SET but reclaims any
memory occupied by removed elements, while `m4_set_dump' is a
faster one-shot action that also deletes the set. No provision is
made for disambiguating members that contain a non-empty SEP as a
substring; use `m4_set_empty' to distinguish between an empty set
and the set containing only the empty string. The order of the
output is unspecified; in the current implementation, part of the
speed of `m4_set_dump' results from using a different output order
than `m4_set_contents'. These macros scale linearly in the size
of the set before memory pruning, and `m4_set_contents([SET],
[SEP])' is faster than `m4_joinall([SEP]m4_set_listc([SET]))'.
m4_set_add_all([a], [1], [2], [3])
=>
m4_set_contents([a], [-])
=>1-2-3
m4_joinall([-]m4_set_listc([a]))
=>1-2-3
m4_set_dump([a], [-])
=>3-2-1
m4_set_contents([a])
=>
m4_set_add([a], [])
=>
m4_set_contents([a], [-])
=>
-- Macro: m4_set_delete (SET)
Delete all elements and memory associated with SET. This is
linear in the set size, and faster than removing one element at a
time.
-- Macro: m4_set_difference (SETA, SETB)
-- Macro: m4_set_intersection (SETA, SETB)
-- Macro: m4_set_union (SETA, SETB)
Compute the relation between SETA and SETB, and output the result
as a list of quoted arguments without duplicates and with a
leading comma. Set difference selects the elements in SETA but
not SETB, intersection selects only elements in both sets, and
union selects elements in either set. These actions are linear in
the sum of the set sizes. The leading comma is necessary to
distinguish between no elements and the empty string as the only
element.
m4_set_add_all([a], [1], [2], [3])
=>
m4_set_add_all([b], [3], [], [4])
=>
m4_set_difference([a], [b])
=>,1,2
m4_set_difference([b], [a])
=>,,4
m4_set_intersection([a], [b])
=>,3
m4_set_union([a], [b])
=>,1,2,3,,4
-- Macro: m4_set_empty (SET, [IF-EMPTY], [IF-ELEMENTS])
Expand IF-EMPTY if the set SET has no elements, otherwise expand
IF-ELEMENTS. This macro operates in constant time. Using this
macro can help disambiguate output from `m4_set_contents' or
`m4_set_list'.
-- Macro: m4_set_foreach (SET, VARIABLE, ACTION)
For each element in the set SET, expand ACTION with the macro
VARIABLE defined as the set element. Behavior is unspecified if
ACTION recursively lists the contents of SET (although listing
other sets is acceptable), or if it modifies the set in any way
other than removing the element currently contained in VARIABLE.
This macro is faster than the corresponding `m4_foreach([VARIABLE],
m4_indir([m4_dquote]m4_set_listc([SET])), [ACTION])', although
`m4_set_map' might be faster still.
m4_set_add_all([a]m4_for([i], [1], [5], [], [,i]))
=>
m4_set_contents([a])
=>12345
m4_set_foreach([a], [i],
[m4_if(m4_eval(i&1), [0], [m4_set_remove([a], i, [i])])])
=>24
m4_set_contents([a])
=>135
-- Macro: m4_set_list (SET)
-- Macro: m4_set_listc (SET)
Produce a list of arguments, where each argument is a quoted
element from the set SET. The variant `m4_set_listc' is
unambiguous, by adding a leading comma if there are any set
elements, whereas the variant `m4_set_list' cannot distinguish
between an empty set and a set containing only the empty string.
These can be directly used in macros that take multiple arguments,
such as `m4_join' or `m4_set_add_all', or wrapped by `m4_dquote'
for macros that take a quoted list, such as `m4_map' or
`m4_foreach'. Any memory occupied by removed elements is
reclaimed during these macros.
m4_set_add_all([a], [1], [2], [3])
=>
m4_set_list([a])
=>1,2,3
m4_set_list([b])
=>
m4_set_listc([b])
=>
m4_count(m4_set_list([b]))
=>1
m4_set_empty([b], [0], [m4_count(m4_set_list([b]))])
=>0
m4_set_add([b], [])
=>
m4_set_list([b])
=>
m4_set_listc([b])
=>,
m4_count(m4_set_list([b]))
=>1
m4_set_empty([b], [0], [m4_count(m4_set_list([b]))])
=>1
-- Macro: m4_set_map (SET, ACTION)
For each element in the set SET, expand ACTION with a single
argument of the set element. Behavior is unspecified if ACTION
recursively lists the contents of SET (although listing other sets
is acceptable), or if it modifies the set in any way other than
removing the element passed as an argument. This macro is faster
than either corresponding counterpart of
`m4_map_args([ACTION]m4_set_listc([SET]))' or
`m4_set_foreach([SET], [var], [ACTION(m4_defn([var]))])'. It is
possible to use `m4_curry' if more than one argument is needed for
ACTION, although it is more efficient to use `m4_set_map_sep' in
that case.
-- Macro: m4_set_map_sep (SET, [PRE], [POST], [SEP])
For each element in the set SET, expand `PRE[element]POST',
additionally expanding SEP between elements. Behavior is
unspecified if the expansion recursively lists the contents of SET
(although listing other sets is acceptable), or if it modifies the
set in any way other than removing the element visited by the
expansion. This macro provides the most efficient means for
non-destructively visiting the elements of a set; in particular,
`m4_set_map([SET], [ACTION])' is equivalent to
`m4_set_map_sep([SET], [ACTION(], [)])'.
-- Macro: m4_set_remove (SET, VALUE, [IF-PRESENT], [IF-ABSENT])
If VALUE is an element in the set SET, then remove it and expand
IF-PRESENT. Otherwise expand IF-ABSENT. This macro operates in
constant time so that multiple removals will scale linearly rather
than quadratically; but when used outside of `m4_set_foreach' or
`m4_set_map', it leaves memory occupied until the set is later
compacted by `m4_set_contents' or `m4_set_list'. Several other
set operations are then less efficient between the time of element
removal and subsequent memory compaction, but still maintain their
guaranteed scaling performance.
-- Macro: m4_set_size (SET)
Expand to the size of the set SET. This implementation operates
in constant time, and is thus more efficient than
`m4_eval(m4_count(m4_set_listc([set])) - 1)'.
File: autoconf.info, Node: Forbidden Patterns, Prev: Set manipulation Macros, Up: Programming in M4sugar
8.3.10 Forbidden Patterns
-------------------------
M4sugar provides a means to define suspicious patterns, patterns
describing tokens which should not be found in the output. For
instance, if an Autoconf `configure' script includes tokens such as
`AC_DEFINE', or `dnl', then most probably something went wrong
(typically a macro was not evaluated because of overquotation).
M4sugar forbids all the tokens matching `^_?m4_' and `^dnl$'.
Additional layers, such as M4sh and Autoconf, add additional forbidden
patterns to the list.
-- Macro: m4_pattern_forbid (PATTERN)
Declare that no token matching PATTERN must be found in the output.
Comments are not checked; this can be a problem if, for instance,
you have some macro left unexpanded after an `#include'. No
consensus is currently found in the Autoconf community, as some
people consider it should be valid to name macros in comments
(which doesn't make sense to the authors of this documentation:
input, such as macros, should be documented by `dnl' comments;
reserving `#'-comments to document the output).
Of course, you might encounter exceptions to these generic rules, for
instance you might have to refer to `$m4_flags'.
-- Macro: m4_pattern_allow (PATTERN)
Any token matching PATTERN is allowed, including if it matches an
`m4_pattern_forbid' pattern.
File: autoconf.info, Node: Debugging via autom4te, Prev: Programming in M4sugar, Up: Programming in M4
8.4 Debugging via autom4te
==========================
At times, it is desirable to see what was happening inside m4, to see
why output was not matching expectations. However, post-processing done
by `autom4te' means that directly using the m4 builtin `m4_traceon' is
likely to interfere with operation. Also, frequent diversion changes
and the concept of forbidden tokens make it difficult to use `m4_defn'
to generate inline comments in the final output.
There are a couple of tools to help with this. One is the use of the
`--trace' option provided by `autom4te' (as well as each of the
programs that wrap `autom4te', such as `autoconf'), in order to inspect
when a macro is called and with which arguments. For example, when
this paragraph was written, the autoconf version could be found by:
$ autoconf --trace=AC_INIT
configure.ac:23:AC_INIT:GNU Autoconf:2.63b.95-3963:bug-autoconf@gnu.org
$ autoconf --trace='AC_INIT:version is $2'
version is 2.63b.95-3963
Another trick is to print out the expansion of various m4
expressions to standard error or to an independent file, with no
further m4 expansion, and without interfering with diversion changes or
the post-processing done to standard output. `m4_errprintn' shows a
given expression on standard error. For example, if you want to see
the expansion of an autoconf primitive or of one of your autoconf
macros, you can do it like this:
$ cat < configure.ac
AC_INIT
m4_errprintn([The definition of AC_DEFINE_UNQUOTED:])
m4_errprintn(m4_defn([AC_DEFINE_UNQUOTED]))
AC_OUTPUT
EOF
$ autoconf
error-->The definition of AC_DEFINE_UNQUOTED:
error-->_AC_DEFINE_Q([], $@)
File: autoconf.info, Node: Programming in M4sh, Next: Writing Autoconf Macros, Prev: Programming in M4, Up: Top
9 Programming in M4sh
*********************
M4sh, pronounced "mash", is aiming at producing portable Bourne shell
scripts. This name was coined by Lars J. Aas, who notes that,
according to the Webster's Revised Unabridged Dictionary (1913):
Mash \Mash\, n. [Akin to G. meisch, maisch, meische, maische,
mash, wash, and prob. to AS. miscian to mix. See "Mix".]
1. A mass of mixed ingredients reduced to a soft pulpy state by
beating or pressure...
2. A mixture of meal or bran and water fed to animals.
3. A mess; trouble. [Obs.] -Beau. & Fl.
M4sh reserves the M4 macro namespace `^_AS_' for internal use, and
the namespace `^AS_' for M4sh macros. It also reserves the shell and
environment variable namespace `^as_', and the here-document delimiter
namespace `^_AS[A-Z]' in the output file. You should not define your
own macros or output shell code that conflicts with these namespaces.
* Menu:
* Common Shell Constructs:: Portability layer for common shell constructs
* Polymorphic Variables:: Support for indirect variable names
* Initialization Macros:: Macros to establish a sane shell environment
* File Descriptor Macros:: File descriptor macros for input and output
File: autoconf.info, Node: Common Shell Constructs, Next: Polymorphic Variables, Up: Programming in M4sh
9.1 Common Shell Constructs
===========================
M4sh provides portable alternatives for some common shell constructs
that unfortunately are not portable in practice.
-- Macro: AS_BOX (TEXT, [CHAR = `-'])
Expand into shell code that will output TEXT surrounded by a box
with CHAR in the top and bottom border. TEXT should not contain a
newline, but may contain shell expansions valid for unquoted
here-documents. CHAR defaults to `-', but can be any character
except `/', `'', `"', `\', `&', or ``'. This is useful for
outputting a comment box into log files to separate distinct
phases of script operation.
-- Macro: AS_CASE (WORD, [PATTERN1], [IF-MATCHED1], ..., [DEFAULT])
Expand into a shell `case' statement, where WORD is matched
against one or more patterns. IF-MATCHED is run if the
corresponding pattern matched WORD, else DEFAULT is run. Avoids
several portability issues (*note Limitations of Shell Builtins:
case.).
-- Macro: AS_DIRNAME (FILE-NAME)
Output the directory portion of FILE-NAME. For example, if
`$file' is `/one/two/three', the command
`dir=`AS_DIRNAME(["$file"])`' sets `dir' to `/one/two'.
This interface may be improved in the future to avoid forks and
losing trailing newlines.
-- Macro: AS_ECHO (WORD)
Emits WORD to the standard output, followed by a newline. WORD
must be a single shell word (typically a quoted string). The
bytes of WORD are output as-is, even if it starts with "-" or
contains "\". Redirections can be placed outside the macro
invocation. This is much more portable than using `echo' (*note
Limitations of Shell Builtins: echo.).
-- Macro: AS_ECHO_N (WORD)
Emits WORD to the standard output, without a following newline.
WORD must be a single shell word (typically a quoted string) and,
for portability, should not include more than one newline. The
bytes of WORD are output as-is, even if it starts with "-" or
contains "\". Redirections can be placed outside the macro
invocation.
-- Macro: AS_ESCAPE (STRING, [CHARS = ``\"$'])
Expands to STRING, with any characters in CHARS escaped with a
backslash (`\'). CHARS should be at most four bytes long, and
only contain characters from the set ``\"$'; however, characters
may be safely listed more than once in CHARS for the sake of
syntax highlighting editors. The current implementation expands
STRING after adding escapes; if STRING contains macro calls that
in turn expand to text needing shell quoting, you can use
`AS_ESCAPE(m4_dquote(m4_expand([string])))'.
The default for CHARS (`\"$`') is the set of characters needing
escapes when STRING will be used literally within double quotes.
One common variant is the set of characters to protect when STRING
will be used literally within back-ticks or an unquoted
here-document (`\$`'). Another common variant is `""', which can
be used to form a double-quoted string containing the same
expansions that would have occurred if STRING were expanded in an
unquoted here-document; however, when using this variant, care
must be taken that STRING does not use double quotes within
complex variable expansions (such as `${foo-`echo "hi"`}') that
would be broken with improper escapes.
This macro is often used with `AS_ECHO'. For an example, observe
the output generated by the shell code generated from this snippet:
foo=bar
AS_ECHO(["AS_ESCAPE(["$foo" = ])AS_ESCAPE(["$foo"], [""])"])
=>"$foo" = "bar"
m4_define([macro], [a, [\b]])
AS_ECHO(["AS_ESCAPE([[macro]])"])
=>macro
AS_ECHO(["AS_ESCAPE([macro])"])
=>a, b
AS_ECHO(["AS_ESCAPE(m4_dquote(m4_expand([macro])))"])
=>a, \b
To escape a string that will be placed within single quotes, use:
m4_bpatsubst([[STRING]], ['], ['\\''])
-- Macro: AS_EXECUTABLE_P (FILE)
Emit code to probe whether FILE is a regular file with executable
permissions (and not a directory with search permissions). The
caller is responsible for quoting FILE.
-- Macro: AS_EXIT ([STATUS = `$?'])
Emit code to exit the shell with STATUS, defaulting to `$?'. This
macro works around shells that see the exit status of the command
prior to `exit' inside a `trap 0' handler (*note Limitations of
Shell Builtins: trap.).
-- Macro: AS_IF (TEST1, [RUN-IF-TRUE1], ..., [RUN-IF-FALSE])
Run shell code TEST1. If TEST1 exits with a zero status then run
shell code RUN-IF-TRUE1, else examine further tests. If no test
exits with a zero status, run shell code RUN-IF-FALSE, with
simplifications if either RUN-IF-TRUE1 or RUN-IF-FALSE is empty.
For example,
AS_IF([test "x$foo" = xyes], [HANDLE_FOO([yes])],
[test "x$foo" != xno], [HANDLE_FOO([maybe])],
[echo foo not specified])
ensures any required macros of `HANDLE_FOO' are expanded before
the first test.
-- Macro: AS_MKDIR_P (FILE-NAME)
Make the directory FILE-NAME, including intervening directories as
necessary. This is equivalent to `mkdir -p -- FILE-NAME', except
that it is portable to older versions of `mkdir' that lack support
for the `-p' option or for the `--' delimiter (*note Limitations
of Usual Tools: mkdir.). Also, `AS_MKDIR_P' succeeds if FILE-NAME
is a symbolic link to an existing directory, even though Posix is
unclear whether `mkdir -p' should succeed in that case. If
creation of FILE-NAME fails, exit the script.
Also see the `AC_PROG_MKDIR_P' macro (*note Particular Programs::).
-- Macro: AS_SET_STATUS (STATUS)
Emit shell code to set the value of `$?' to STATUS, as efficiently
as possible. However, this is not guaranteed to abort a shell
running with `set -e' (*note Limitations of Shell Builtins: set.).
This should also be used at the end of a complex shell function
instead of `return' (*note Shell Functions::) to avoid a DJGPP
shell bug.
-- Macro: AS_TR_CPP (EXPRESSION)
Transform EXPRESSION into a valid right-hand side for a C
`#define'. For example:
# This outputs "#define HAVE_CHAR_P 1".
# Notice the m4 quoting around #, to prevent an m4 comment
type="char *"
echo "[#]define AS_TR_CPP([HAVE_$type]) 1"
-- Macro: AS_TR_SH (EXPRESSION)
Transform EXPRESSION into shell code that generates a valid shell
variable name. The result is literal when possible at m4 time,
but must be used with `eval' if EXPRESSION causes shell
indirections. For example:
# This outputs "Have it!".
header="sys/some file.h"
eval AS_TR_SH([HAVE_$header])=yes
if test "x$HAVE_sys_some_file_h" = xyes; then echo "Have it!"; fi
-- Macro: AS_SET_CATFILE (VAR, DIR, FILE)
Set the polymorphic shell variable VAR to DIR/FILE, but optimizing
the common cases (DIR or FILE is `.', FILE is absolute, etc.).
-- Macro: AS_UNSET (VAR)
Unsets the shell variable VAR, working around bugs in older shells
(*note Limitations of Shell Builtins: unset.). VAR can be a
literal or indirect variable name.
-- Macro: AS_VERSION_COMPARE (VERSION-1, VERSION-2, [ACTION-IF-LESS],
[ACTION-IF-EQUAL], [ACTION-IF-GREATER])
Compare two strings VERSION-1 and VERSION-2, possibly containing
shell variables, as version strings, and expand ACTION-IF-LESS,
ACTION-IF-EQUAL, or ACTION-IF-GREATER depending upon the result.
The algorithm to compare is similar to the one used by strverscmp
in glibc (*note String/Array Comparison: (libc)String/Array
Comparison.).
File: autoconf.info, Node: Polymorphic Variables, Next: Initialization Macros, Prev: Common Shell Constructs, Up: Programming in M4sh
9.2 Support for indirect variable names
=======================================
Often, it is convenient to write a macro that will emit shell code
operating on a shell variable. The simplest case is when the variable
name is known. But a more powerful idiom is writing shell code that can
work through an indirection, where another variable or command
substitution produces the name of the variable to actually manipulate.
M4sh supports the notion of polymorphic shell variables, making it easy
to write a macro that can deal with either literal or indirect variable
names and output shell code appropriate for both use cases. Behavior is
undefined if expansion of an indirect variable does not result in a
literal variable name.
-- Macro: AS_LITERAL_IF (EXPRESSION, [IF-LITERAL], [IF-NOT],
[IF-SIMPLE-REF = `IF-NOT'])
-- Macro: AS_LITERAL_WORD_IF (EXPRESSION, [IF-LITERAL], [IF-NOT],
[IF-SIMPLE-REF = `IF-NOT'])
If the expansion of EXPRESSION is definitely a shell literal,
expand IF-LITERAL. If the expansion of EXPRESSION looks like it
might contain shell indirections (such as `$var' or ``expr`'),
then IF-NOT is expanded. Sometimes, it is possible to output
optimized code if EXPRESSION consists only of shell variable
expansions (such as `${var}'), in which case IF-SIMPLE-REF can be
provided; but defaulting to IF-NOT should always be safe.
`AS_LITERAL_WORD_IF' only expands IF-LITERAL if EXPRESSION looks
like a single shell word, containing no whitespace; while
`AS_LITERAL_IF' allows whitespace in EXPRESSION.
In order to reduce the time spent recognizing whether an
EXPRESSION qualifies as a literal or a simple indirection, the
implementation is somewhat conservative: EXPRESSION must be a
single shell word (possibly after stripping whitespace),
consisting only of bytes that would have the same meaning whether
unquoted or enclosed in double quotes (for example, `a.b' results
in IF-LITERAL, even though it is not a valid shell variable name;
while both `'a'' and `[$]' result in IF-NOT, because they behave
differently than `"'a'"' and `"[$]"'). This macro can be used in
contexts for recognizing portable file names (such as in the
implementation of `AC_LIBSOURCE'), or coupled with some
transliterations for forming valid variable names (such as in the
implementation of `AS_TR_SH', which uses an additional
`m4_translit' to convert `.' to `_').
This example shows how to read the contents of the shell variable
`bar', exercising all three arguments to `AS_LITERAL_IF'. It
results in a script that will output the line `hello' three times.
AC_DEFUN([MY_ACTION],
[AS_LITERAL_IF([$1],
[echo "$$1"],
[AS_VAR_COPY([var], [$1])
echo "$var"],
[eval 'echo "$'"$1"\"])])
foo=bar bar=hello
MY_ACTION([bar])
MY_ACTION([`echo bar`])
MY_ACTION([$foo])
-- Macro: AS_VAR_APPEND (VAR, TEXT)
Emit shell code to append the shell expansion of TEXT to the end
of the current contents of the polymorphic shell variable VAR,
taking advantage of shells that provide the `+=' extension for more
efficient scaling.
For situations where the final contents of VAR are relatively
short (less than 256 bytes), it is more efficient to use the
simpler code sequence of `VAR=${VAR}TEXT' (or its polymorphic
equivalent of `AS_VAR_COPY([t], [VAR])' and `AS_VAR_SET([VAR],
["$t"TEXT])'). But in the case when the script will be repeatedly
appending text into `var', issues of scaling start to become
apparent. A naive implementation requires execution time linear
to the length of the current contents of VAR as well as the length
of TEXT for a single append, for an overall quadratic scaling with
multiple appends. This macro takes advantage of shells which
provide the extension `VAR+=TEXT', which can provide amortized
constant time for a single append, for an overall linear scaling
with multiple appends. Note that unlike `AS_VAR_SET', this macro
requires that TEXT be quoted properly to avoid field splitting and
file name expansion.
-- Macro: AS_VAR_ARITH (VAR, EXPRESSION)
Emit shell code to compute the arithmetic expansion of EXPRESSION,
assigning the result as the contents of the polymorphic shell
variable VAR. The code takes advantage of shells that provide
`$(())' for fewer forks, but uses `expr' as a fallback.
Therefore, the syntax for a valid EXPRESSION is rather limited:
all operators must occur as separate shell arguments and with
proper quoting, there is no portable equality operator, all
variables containing numeric values must be expanded prior to the
computation, all numeric values must be provided in decimal
without leading zeroes, and the first shell argument should not be
a negative number. In the following example, this snippet will
print `(2+3)*4 == 20'.
bar=3
AS_VAR_ARITH([foo], [\( 2 + $bar \) \* 4])
echo "(2+$bar)*4 == $foo"
-- Macro: AS_VAR_COPY (DEST, SOURCE)
Emit shell code to assign the contents of the polymorphic shell
variable SOURCE to the polymorphic shell variable DEST. For
example, executing this M4sh snippet will output `bar hi':
foo=bar bar=hi
AS_VAR_COPY([a], [foo])
AS_VAR_COPY([b], [$foo])
echo "$a $b"
When it is necessary to access the contents of an indirect variable
inside a shell double-quoted context, the recommended idiom is to
first copy the contents into a temporary literal shell variable.
for header in stdint_h inttypes_h ; do
AS_VAR_COPY([var], [ac_cv_header_$header])
echo "$header detected: $var"
done
-- Macro: AS_VAR_IF (VAR, [WORD], [IF-EQUAL], [IF-NOT-EQUAL])
Output a shell conditional statement. If the contents of the
polymorphic shell variable VAR match the string WORD, execute
IF-EQUAL; otherwise execute IF-NOT-EQUAL. WORD must be a single
shell word (typically a quoted string). Avoids shell bugs if an
interrupt signal arrives while a command substitution in VAR is
being expanded.
-- Macro: AS_VAR_PUSHDEF (M4-NAME, VALUE)
-- Macro: AS_VAR_POPDEF (M4-NAME)
A common M4sh idiom involves composing shell variable names from
an m4 argument (for example, writing a macro that uses a cache
variable). VALUE can be an arbitrary string, which will be
transliterated into a valid shell name by `AS_TR_SH'. In order to
access the composed variable name based on VALUE, it is easier to
declare a temporary m4 macro M4-NAME with `AS_VAR_PUSHDEF', then
use that macro as the argument to subsequent `AS_VAR' macros as a
polymorphic variable name, and finally free the temporary macro
with `AS_VAR_POPDEF'. These macros are often followed with `dnl',
to avoid excess newlines in the output.
Here is an involved example, that shows the power of writing
macros that can handle composed shell variable names:
m4_define([MY_CHECK_HEADER],
[AS_VAR_PUSHDEF([my_Header], [ac_cv_header_$1])dnl
AS_VAR_IF([my_Header], [yes], [echo "header $1 detected"])dnl
AS_VAR_POPDEF([my_Header])dnl
])
MY_CHECK_HEADER([stdint.h])
for header in inttypes.h stdlib.h ; do
MY_CHECK_HEADER([$header])
done
In the above example, `MY_CHECK_HEADER' can operate on polymorphic
variable names. In the first invocation, the m4 argument is
`stdint.h', which transliterates into a literal `stdint_h'. As a
result, the temporary macro `my_Header' expands to the literal
shell name `ac_cv_header_stdint_h'. In the second invocation, the
m4 argument to `MY_CHECK_HEADER' is `$header', and the temporary
macro `my_Header' expands to the indirect shell name
`$as_my_Header'. During the shell execution of the for loop, when
`$header' contains `inttypes.h', then `$as_my_Header' contains
`ac_cv_header_inttypes_h'. If this script is then run on a
platform where all three headers have been previously detected, the
output of the script will include:
header stdint.h detected
header inttypes.h detected
header stdlib.h detected
-- Macro: AS_VAR_SET (VAR, [VALUE])
Emit shell code to assign the contents of the polymorphic shell
variable VAR to the shell expansion of VALUE. VALUE is not
subject to field splitting or file name expansion, so if command
substitution is used, it may be done with ``""`' rather than using
an intermediate variable (*note Shell Substitutions::). However,
VALUE does undergo rescanning for additional macro names; behavior
is unspecified if late expansion results in any shell
meta-characters.
-- Macro: AS_VAR_SET_IF (VAR, [IF-SET], [IF-UNDEF])
Emit a shell conditional statement, which executes IF-SET if the
polymorphic shell variable `var' is set to any value, and IF-UNDEF
otherwise.
-- Macro: AS_VAR_TEST_SET (VAR)
Emit a shell statement that results in a successful exit status
only if the polymorphic shell variable `var' is set.
File: autoconf.info, Node: Initialization Macros, Next: File Descriptor Macros, Prev: Polymorphic Variables, Up: Programming in M4sh
9.3 Initialization Macros
=========================
-- Macro: AS_BOURNE_COMPATIBLE
Set up the shell to be more compatible with the Bourne shell as
standardized by Posix, if possible. This may involve setting
environment variables, or setting options, or similar
implementation-specific actions. This macro is deprecated, since
`AS_INIT' already invokes it.
-- Macro: AS_INIT
Initialize the M4sh environment. This macro calls `m4_init', then
outputs the `#! /bin/sh' line, a notice about where the output was
generated from, and code to sanitize the environment for the rest
of the script. Among other initializations, this sets `SHELL' to
the shell chosen to run the script (*note CONFIG_SHELL::), and
`LC_ALL' to ensure the C locale. Finally, it changes the current
diversion to `BODY'. `AS_INIT' is called automatically by
`AC_INIT' and `AT_INIT', so shell code in `configure',
`config.status', and `testsuite' all benefit from a sanitized
shell environment.
-- Macro: AS_INIT_GENERATED (FILE, [COMMENT])
Emit shell code to start the creation of a subsidiary shell script
in FILE, including changing FILE to be executable. This macro
populates the child script with information learned from the parent
(thus, the emitted code is equivalent in effect, but more
efficient, than the code output by `AS_INIT',
`AS_BOURNE_COMPATIBLE', and `AS_SHELL_SANITIZE'). If present,
COMMENT is output near the beginning of the child, prior to the
shell initialization code, and is subject to parameter expansion,
command substitution, and backslash quote removal. The parent
script should check the exit status after this macro, in case FILE
could not be properly created (for example, if the disk was full).
If successfully created, the parent script can then proceed to
append additional M4sh constructs into the child script.
Note that the child script starts life without a log file open, so
if the parent script uses logging (*note AS_MESSAGE_LOG_FD::), you
must temporarily disable any attempts to use the log file until
after emitting code to open a log within the child. On the other
hand, if the parent script has `AS_MESSAGE_FD' redirected
somewhere besides `1', then the child script already has code that
copies stdout to that descriptor. Currently, the suggested idiom
for writing a M4sh shell script from within another script is:
AS_INIT_GENERATED([FILE], [[# My child script.
]]) || { AS_ECHO(["Failed to create child script"]); AS_EXIT; }
m4_pushdef([AS_MESSAGE_LOG_FD])dnl
cat >> "FILE" <
File: autoconf.info, Node: File Descriptor Macros, Prev: Initialization Macros, Up: Programming in M4sh
9.4 File Descriptor Macros
==========================
The following macros define file descriptors used to output messages
(or input values) from `configure' scripts. For example:
echo "$wombats found" >&AS_MESSAGE_LOG_FD
echo 'Enter desired kangaroo count:' >&AS_MESSAGE_FD
read kangaroos
File: autoconf.info, Node: Writing Autoconf Macros, Next: Portable Shell, Prev: Programming in M4sh, Up: Top
10 Writing Autoconf Macros
**************************
When you write a feature test that could be applicable to more than one
software package, the best thing to do is encapsulate it in a new macro.
Here are some instructions and guidelines for writing Autoconf macros.
* Menu:
* Macro Definitions:: Basic format of an Autoconf macro
* Macro Names:: What to call your new macros
* Reporting Messages:: Notifying `autoconf' users
* Dependencies Between Macros:: What to do when macros depend on other macros
* Obsoleting Macros:: Warning about old ways of doing things
* Coding Style:: Writing Autoconf macros a` la Autoconf
File: autoconf.info, Node: Macro Definitions, Next: Macro Names, Up: Writing Autoconf Macros
10.1 Macro Definitions
======================
-- Macro: AC_DEFUN (NAME, [BODY])
Autoconf macros are defined using the `AC_DEFUN' macro, which is
similar to the M4 builtin `m4_define' macro; this creates a macro
named NAME and with BODY as its expansion. In addition to
defining a macro, `AC_DEFUN' adds to it some code that is used to
constrain the order in which macros are called, while avoiding
redundant output (*note Prerequisite Macros::).
An Autoconf macro definition looks like this:
AC_DEFUN(MACRO-NAME, MACRO-BODY)
You can refer to any arguments passed to the macro as `$1', `$2',
etc. *Note How to define new macros: (m4.info)Definitions, for more
complete information on writing M4 macros.
Most macros fall in one of two general categories. The first
category includes macros which take arguments, in order to generate
output parameterized by those arguments. Macros in this category are
designed to be directly expanded, often multiple times, and should not
be used as the argument to `AC_REQUIRE'. The other category includes
macros which are shorthand for a fixed block of text, and therefore do
not take arguments. For this category of macros, directly expanding
the macro multiple times results in redundant output, so it is more
common to use the macro as the argument to `AC_REQUIRE', or to declare
the macro with `AC_DEFUN_ONCE' (*note One-Shot Macros::).
Be sure to properly quote both the MACRO-BODY _and_ the MACRO-NAME
to avoid any problems if the macro happens to have been previously
defined.
Each macro should have a header comment that gives its prototype,
and a brief description. When arguments have default values, display
them in the prototype. For example:
# AC_MSG_ERROR(ERROR, [EXIT-STATUS = 1])
# --------------------------------------
m4_define([AC_MSG_ERROR],
[{ AS_MESSAGE([error: $1], [2])
exit m4_default([$2], [1]); }])
Comments about the macro should be left in the header comment. Most
other comments make their way into `configure', so just keep using `#'
to introduce comments.
If you have some special comments about pure M4 code, comments that
make no sense in `configure' and in the header comment, then use the
builtin `dnl': it causes M4 to discard the text through the next
newline.
Keep in mind that `dnl' is rarely needed to introduce comments;
`dnl' is more useful to get rid of the newlines following macros that
produce no output, such as `AC_REQUIRE'.
Public third-party macros need to use `AC_DEFUN', and not
`m4_define', in order to be found by `aclocal' (*note Extending
aclocal: (automake)Extending aclocal.). Additionally, if it is ever
determined that a macro should be made obsolete, it is easy to convert
from `AC_DEFUN' to `AU_DEFUN' in order to have `autoupdate' assist the
user in choosing a better alternative, but there is no corresponding
way to make `m4_define' issue an upgrade notice (*note AU_DEFUN::).
There is another subtle, but important, difference between using
`m4_define' and `AC_DEFUN': only the former is unaffected by
`AC_REQUIRE'. When writing a file, it is always safe to replace a
block of text with a `m4_define' macro that will expand to the same
text. But replacing a block of text with an `AC_DEFUN' macro with the
same content does not necessarily give the same results, because it
changes the location where any embedded but unsatisfied `AC_REQUIRE'
invocations within the block will be expanded. For an example of this,
see *note Expanded Before Required::.
File: autoconf.info, Node: Macro Names, Next: Reporting Messages, Prev: Macro Definitions, Up: Writing Autoconf Macros
10.2 Macro Names
================
All of the public Autoconf macros have all-uppercase names in the
namespace `^AC_' to prevent them from accidentally conflicting with
other text; Autoconf also reserves the namespace `^_AC_' for internal
macros. All shell variables that they use for internal purposes have
mostly-lowercase names starting with `ac_'. Autoconf also uses
here-document delimiters in the namespace `^_AC[A-Z]'. During
`configure', files produced by Autoconf make heavy use of the file
system namespace `^conf'.
Since Autoconf is built on top of M4sugar (*note Programming in
M4sugar::) and M4sh (*note Programming in M4sh::), you must also be
aware of those namespaces (`^_?\(m4\|AS\)_'). And since `configure.ac'
is also designed to be scanned by Autoheader, Autoscan, Autoupdate, and
Automake, you should be aware of the `^_?A[HNUM]_' namespaces. In
general, you _should not use_ the namespace of a package that does not
own the macro or shell code you are writing.
To ensure that your macros don't conflict with present or future
Autoconf macros, you should prefix your own macro names and any shell
variables they use with some other sequence. Possibilities include your
initials, or an abbreviation for the name of your organization or
software package. Historically, people have not always followed the
rule of using a namespace appropriate for their package, and this has
made it difficult for determining the origin of a macro (and where to
report bugs about that macro), as well as difficult for the true
namespace owner to add new macros without interference from pre-existing
uses of third-party macros. Perhaps the best example of this confusion
is the `AM_GNU_GETTEXT' macro, which belongs, not to Automake, but to
Gettext.
Most of the Autoconf macros' names follow a structured naming
convention that indicates the kind of feature check by the name. The
macro names consist of several words, separated by underscores, going
from most general to most specific. The names of their cache variables
use the same convention (*note Cache Variable Names::, for more
information on them).
The first word of the name after the namespace initials (such as
`AC_') usually tells the category of the feature being tested. Here
are the categories used in Autoconf for specific test macros, the kind
of macro that you are more likely to write. They are also used for
cache variables, in all-lowercase. Use them where applicable; where
they're not, invent your own categories.
`C'
C language builtin features.
`DECL'
Declarations of C variables in header files.
`FUNC'
Functions in libraries.
`GROUP'
Posix group owners of files.
`HEADER'
Header files.
`LIB'
C libraries.
`PROG'
The base names of programs.
`MEMBER'
Members of aggregates.
`SYS'
Operating system features.
`TYPE'
C builtin or declared types.
`VAR'
C variables in libraries.
After the category comes the name of the particular feature being
tested. Any further words in the macro name indicate particular aspects
of the feature. For example, `AC_PROG_CC_STDC' checks whether the C
compiler supports ISO Standard C.
An internal macro should have a name that starts with an underscore;
Autoconf internals should therefore start with `_AC_'. Additionally, a
macro that is an internal subroutine of another macro should have a
name that starts with an underscore and the name of that other macro,
followed by one or more words saying what the internal macro does. For
example, `AC_PATH_X' has internal macros `_AC_PATH_X_XMKMF' and
`_AC_PATH_X_DIRECT'.
File: autoconf.info, Node: Reporting Messages, Next: Dependencies Between Macros, Prev: Macro Names, Up: Writing Autoconf Macros
10.3 Reporting Messages
=======================
When macros statically diagnose abnormal situations, benign or fatal, it
is possible to make `autoconf' detect the problem, and refuse to create
`configure' in the case of an error. The macros in this section are
considered obsolescent, and new code should use M4sugar macros for this
purpose, see *note Diagnostic Macros::.
On the other hand, it is possible to want to detect errors when
`configure' is run, which are dependent on the environment of the user
rather than the maintainer. For dynamic diagnostics, see *note
Printing Messages::.
-- Macro: AC_DIAGNOSE (CATEGORY, MESSAGE)
Report MESSAGE as a warning (or as an error if requested by the
user) if warnings of the CATEGORY are turned on. This macro is
obsolescent; you are encouraged to use:
m4_warn([CATEGORY], [MESSAGE])
instead. *Note m4_warn::, for more details, including valid
CATEGORY names.
-- Macro: AC_WARNING (MESSAGE)
Report MESSAGE as a syntax warning. This macro is obsolescent;
you are encouraged to use:
m4_warn([syntax], [MESSAGE])
instead. *Note m4_warn::, for more details, as well as better
finer-grained categories of warnings (not all problems have to do
with syntax).
-- Macro: AC_FATAL (MESSAGE)
Report a severe error MESSAGE, and have `autoconf' die. This
macro is obsolescent; you are encouraged to use:
m4_fatal([MESSAGE])
instead. *Note m4_fatal::, for more details.
When the user runs `autoconf -W error', warnings from `m4_warn'
(including those issued through `AC_DIAGNOSE' and `AC_WARNING') are
reported as errors, see *note autoconf Invocation::.
File: autoconf.info, Node: Dependencies Between Macros, Next: Obsoleting Macros, Prev: Reporting Messages, Up: Writing Autoconf Macros
10.4 Dependencies Between Macros
================================
Some Autoconf macros depend on other macros having been called first in
order to work correctly. Autoconf provides a way to ensure that certain
macros are called if needed and a way to warn the user if macros are
called in an order that might cause incorrect operation.
* Menu:
* Prerequisite Macros:: Ensuring required information
* Suggested Ordering:: Warning about possible ordering problems
* One-Shot Macros:: Ensuring a macro is called only once
File: autoconf.info, Node: Prerequisite Macros, Next: Suggested Ordering, Up: Dependencies Between Macros
10.4.1 Prerequisite Macros
--------------------------
A macro that you write might need to use values that have previously
been computed by other macros. For example, `AC_DECL_YYTEXT' examines
the output of `flex' or `lex', so it depends on `AC_PROG_LEX' having
been called first to set the shell variable `LEX'.
Rather than forcing the user of the macros to keep track of the
dependencies between them, you can use the `AC_REQUIRE' macro to do it
automatically. `AC_REQUIRE' can ensure that a macro is only called if
it is needed, and only called once.
-- Macro: AC_REQUIRE (MACRO-NAME)
If the M4 macro MACRO-NAME has not already been called, call it
(without any arguments). Make sure to quote MACRO-NAME with
square brackets. MACRO-NAME must have been defined using
`AC_DEFUN' or else contain a call to `AC_PROVIDE' to indicate that
it has been called.
`AC_REQUIRE' must be used inside a macro defined by `AC_DEFUN'; it
must not be called from the top level. Also, it does not make
sense to require a macro that takes parameters.
`AC_REQUIRE' is often misunderstood. It really implements
dependencies between macros in the sense that if one macro depends upon
another, the latter is expanded _before_ the body of the former. To be
more precise, the required macro is expanded before the outermost
defined macro in the current expansion stack. In particular,
`AC_REQUIRE([FOO])' is not replaced with the body of `FOO'. For
instance, this definition of macros:
AC_DEFUN([TRAVOLTA],
[test "$body_temperature_in_celsius" -gt "38" &&
dance_floor=occupied])
AC_DEFUN([NEWTON_JOHN],
[test "x$hair_style" = xcurly &&
dance_floor=occupied])
AC_DEFUN([RESERVE_DANCE_FLOOR],
[if date | grep '^Sat.*pm' >/dev/null 2>&1; then
AC_REQUIRE([TRAVOLTA])
AC_REQUIRE([NEWTON_JOHN])
fi])
with this `configure.ac'
AC_INIT([Dance Manager], [1.0], [bug-dance@example.org])
RESERVE_DANCE_FLOOR
if test "x$dance_floor" = xoccupied; then
AC_MSG_ERROR([cannot pick up here, let's move])
fi
does not leave you with a better chance to meet a kindred soul at other
times than Saturday night since it expands into:
test "$body_temperature_in_Celsius" -gt "38" &&
dance_floor=occupied
test "x$hair_style" = xcurly &&
dance_floor=occupied
fi
if date | grep '^Sat.*pm' >/dev/null 2>&1; then
fi
This behavior was chosen on purpose: (i) it prevents messages in
required macros from interrupting the messages in the requiring macros;
(ii) it avoids bad surprises when shell conditionals are used, as in:
if ...; then
AC_REQUIRE([SOME_CHECK])
fi
...
SOME_CHECK
However, this implementation can lead to another class of problems.
Consider the case where an outer macro first expands, then indirectly
requires, an inner macro:
AC_DEFUN([TESTA], [[echo in A
if test -n "$SEEN_A" ; then echo duplicate ; fi
SEEN_A=:]])
AC_DEFUN([TESTB], [AC_REQUIRE([TESTA])[echo in B
if test -z "$SEEN_A" ; then echo bug ; fi]])
AC_DEFUN([TESTC], [AC_REQUIRE([TESTB])[echo in C]])
AC_DEFUN([OUTER], [[echo in OUTER]
TESTA
TESTC])
OUTER
Prior to Autoconf 2.64, the implementation of `AC_REQUIRE' recognized
that `TESTB' needed to be hoisted prior to the expansion of `OUTER',
but because `TESTA' had already been directly expanded, it failed to
hoist `TESTA'. Therefore, the expansion of `TESTB' occurs prior to its
prerequisites, leading to the following output:
in B
bug
in OUTER
in A
in C
Newer Autoconf is smart enough to recognize this situation, and hoists
`TESTA' even though it has already been expanded, but issues a syntax
warning in the process. This is because the hoisted expansion of
`TESTA' defeats the purpose of using `AC_REQUIRE' to avoid redundant
code, and causes its own set of problems if the hoisted macro is not
idempotent:
in A
in B
in OUTER
in A
duplicate
in C
The bug is not in Autoconf, but in the macro definitions. If you
ever pass a particular macro name to `AC_REQUIRE', then you are implying
that the macro only needs to be expanded once. But to enforce this,
either the macro must be declared with `AC_DEFUN_ONCE' (although this
only helps in Autoconf 2.64 or newer), or all uses of that macro should
be through `AC_REQUIRE'; directly expanding the macro defeats the point
of using `AC_REQUIRE' to eliminate redundant expansion. In the
example, this rule of thumb was violated because `TESTB' requires
`TESTA' while `OUTER' directly expands it. One way of fixing the bug
is to factor `TESTA' into two macros, the portion designed for direct
and repeated use (here, named `TESTA'), and the portion designed for
one-shot output and used only inside `AC_REQUIRE' (here, named
`TESTA_PREREQ'). Then, by fixing all clients to use the correct
calling convention according to their needs:
AC_DEFUN([TESTA], [AC_REQUIRE([TESTA_PREREQ])[echo in A]])
AC_DEFUN([TESTA_PREREQ], [[echo in A_PREREQ
if test -n "$SEEN_A" ; then echo duplicate ; fi
SEEN_A=:]])
AC_DEFUN([TESTB], [AC_REQUIRE([TESTA_PREREQ])[echo in B
if test -z "$SEEN_A" ; then echo bug ; fi]])
AC_DEFUN([TESTC], [AC_REQUIRE([TESTB])[echo in C]])
AC_DEFUN([OUTER], [[echo in OUTER]
TESTA
TESTC])
OUTER
the resulting output will then obey all dependency rules and avoid any
syntax warnings, whether the script is built with old or new Autoconf
versions:
in A_PREREQ
in B
in OUTER
in A
in C
The helper macros `AS_IF' and `AS_CASE' may be used to enforce
expansion of required macros outside of shell conditional constructs.
You are furthermore encouraged, although not required, to put all
`AC_REQUIRE' calls at the beginning of a macro. You can use `dnl' to
avoid the empty lines they leave.
File: autoconf.info, Node: Suggested Ordering, Next: One-Shot Macros, Prev: Prerequisite Macros, Up: Dependencies Between Macros
10.4.2 Suggested Ordering
-------------------------
Some macros should be run before another macro if both are called, but
neither _requires_ that the other be called. For example, a macro that
changes the behavior of the C compiler should be called before any
macros that run the C compiler. Many of these dependencies are noted in
the documentation.
Autoconf provides the `AC_BEFORE' macro to warn users when macros
with this kind of dependency appear out of order in a `configure.ac'
file. The warning occurs when creating `configure' from
`configure.ac', not when running `configure'.
For example, `AC_PROG_CPP' checks whether the C compiler can run the
C preprocessor when given the `-E' option. It should therefore be
called after any macros that change which C compiler is being used,
such as `AC_PROG_CC'. So `AC_PROG_CC' contains:
AC_BEFORE([$0], [AC_PROG_CPP])dnl
This warns the user if a call to `AC_PROG_CPP' has already occurred
when `AC_PROG_CC' is called.
-- Macro: AC_BEFORE (THIS-MACRO-NAME, CALLED-MACRO-NAME)
Make M4 print a warning message to the standard error output if
CALLED-MACRO-NAME has already been called. THIS-MACRO-NAME should
be the name of the macro that is calling `AC_BEFORE'. The macro
CALLED-MACRO-NAME must have been defined using `AC_DEFUN' or else
contain a call to `AC_PROVIDE' to indicate that it has been called.
File: autoconf.info, Node: One-Shot Macros, Prev: Suggested Ordering, Up: Dependencies Between Macros
10.4.3 One-Shot Macros
----------------------
Some macros should be called only once, either because calling them
multiple time is unsafe, or because it is bad style. For instance
Autoconf ensures that `AC_CANONICAL_BUILD' and cousins (*note
Canonicalizing::) are evaluated only once, because it makes no sense to
run these expensive checks more than once. Such one-shot macros can be
defined using `AC_DEFUN_ONCE'.
-- Macro: AC_DEFUN_ONCE (MACRO-NAME, MACRO-BODY)
Declare macro MACRO-NAME like `AC_DEFUN' would (*note Macro
Definitions::), but add additional logic that guarantees that only
the first use of the macro (whether by direct expansion or
`AC_REQUIRE') causes an expansion of MACRO-BODY; the expansion
will occur before the start of any enclosing macro defined by
`AC_DEFUN'. Subsequent expansions are silently ignored.
Generally, it does not make sense for MACRO-BODY to use parameters
such as `$1'.
Prior to Autoconf 2.64, a macro defined by `AC_DEFUN_ONCE' would
emit a warning if it was directly expanded a second time, so for
portability, it is better to use `AC_REQUIRE' than direct invocation of
MACRO-NAME inside a macro defined by `AC_DEFUN' (*note Prerequisite
Macros::).
File: autoconf.info, Node: Obsoleting Macros, Next: Coding Style, Prev: Dependencies Between Macros, Up: Writing Autoconf Macros
10.5 Obsoleting Macros
======================
Configuration and portability technology has evolved over the years.
Often better ways of solving a particular problem are developed, or
ad-hoc approaches are systematized. This process has occurred in many
parts of Autoconf. One result is that some of the macros are now
considered "obsolete"; they still work, but are no longer considered
the best thing to do, hence they should be replaced with more modern
macros. Ideally, `autoupdate' should replace the old macro calls with
their modern implementation.
Autoconf provides a simple means to obsolete a macro.
-- Macro: AU_DEFUN (OLD-MACRO, IMPLEMENTATION, [MESSAGE])
Define OLD-MACRO as IMPLEMENTATION. The only difference with
`AC_DEFUN' is that the user is warned that OLD-MACRO is now
obsolete.
If she then uses `autoupdate', the call to OLD-MACRO is replaced
by the modern IMPLEMENTATION. MESSAGE should include information
on what to do after running `autoupdate'; `autoupdate' prints it
as a warning, and includes it in the updated `configure.ac' file.
The details of this macro are hairy: if `autoconf' encounters an
`AU_DEFUN'ed macro, all macros inside its second argument are
expanded as usual. However, when `autoupdate' is run, only M4 and
M4sugar macros are expanded here, while all other macros are
disabled and appear literally in the updated `configure.ac'.
-- Macro: AU_ALIAS (OLD-NAME, NEW-NAME)
Used if the OLD-NAME is to be replaced by a call to NEW-MACRO with
the same parameters. This happens for example if the macro was
renamed.
File: autoconf.info, Node: Coding Style, Prev: Obsoleting Macros, Up: Writing Autoconf Macros
10.6 Coding Style
=================
The Autoconf macros follow a strict coding style. You are encouraged to
follow this style, especially if you intend to distribute your macro,
either by contributing it to Autoconf itself or the Autoconf Macro
Archive (http://www.gnu.org/software/autoconf-archive/), or by other
means.
The first requirement is to pay great attention to the quotation.
For more details, see *note Autoconf Language::, and *note M4
Quotation::.
Do not try to invent new interfaces. It is likely that there is a
macro in Autoconf that resembles the macro you are defining: try to
stick to this existing interface (order of arguments, default values,
etc.). We _are_ conscious that some of these interfaces are not
perfect; nevertheless, when harmless, homogeneity should be preferred
over creativity.
Be careful about clashes both between M4 symbols and between shell
variables.
If you stick to the suggested M4 naming scheme (*note Macro Names::),
you are unlikely to generate conflicts. Nevertheless, when you need to
set a special value, _avoid using a regular macro name_; rather, use an
"impossible" name. For instance, up to version 2.13, the macro
`AC_SUBST' used to remember what SYMBOL macros were already defined by
setting `AC_SUBST_SYMBOL', which is a regular macro name. But since
there is a macro named `AC_SUBST_FILE', it was just impossible to
`AC_SUBST(FILE)'! In this case, `AC_SUBST(SYMBOL)' or
`_AC_SUBST(SYMBOL)' should have been used (yes, with the parentheses).
No Autoconf macro should ever enter the user-variable name space;
i.e., except for the variables that are the actual result of running the
macro, all shell variables should start with `ac_'. In addition, small
macros or any macro that is likely to be embedded in other macros
should be careful not to use obvious names.
Do not use `dnl' to introduce comments: most of the comments you are
likely to write are either header comments which are not output anyway,
or comments that should make their way into `configure'. There are
exceptional cases where you do want to comment special M4 constructs,
in which case `dnl' is right, but keep in mind that it is unlikely.
M4 ignores the leading blanks and newlines before each argument.
Use this feature to indent in such a way that arguments are (more or
less) aligned with the opening parenthesis of the macro being called.
For instance, instead of
AC_CACHE_CHECK(for EMX OS/2 environment,
ac_cv_emxos2,
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, [return __EMX__;])],
[ac_cv_emxos2=yes], [ac_cv_emxos2=no])])
write
AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2],
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])],
[ac_cv_emxos2=yes],
[ac_cv_emxos2=no])])
or even
AC_CACHE_CHECK([for EMX OS/2 environment],
[ac_cv_emxos2],
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([],
[return __EMX__;])],
[ac_cv_emxos2=yes],
[ac_cv_emxos2=no])])
When using `AC_RUN_IFELSE' or any macro that cannot work when
cross-compiling, provide a pessimistic value (typically `no').
Feel free to use various tricks to prevent auxiliary tools, such as
syntax-highlighting editors, from behaving improperly. For instance,
instead of:
m4_bpatsubst([$1], [$"])
use
m4_bpatsubst([$1], [$""])
so that Emacsen do not open an endless "string" at the first quote.
For the same reasons, avoid:
test $[#] != 0
and use:
test $[@%:@] != 0
Otherwise, the closing bracket would be hidden inside a `#'-comment,
breaking the bracket-matching highlighting from Emacsen. Note the
preferred style to escape from M4: `$[1]', `$[@]', etc. Do not escape
when it is unnecessary. Common examples of useless quotation are
`[$]$1' (write `$$1'), `[$]var' (use `$var'), etc. If you add
portability issues to the picture, you'll prefer `${1+"$[@]"}' to
`"[$]@"', and you'll prefer do something better than hacking Autoconf
`:-)'.
When using `sed', don't use `-e' except for indenting purposes.
With the `s' and `y' commands, the preferred separator is `/' unless
`/' itself might appear in the pattern or replacement, in which case
you should use `|', or optionally `,' if you know the pattern and
replacement cannot contain a file name. If none of these characters
will do, choose a printable character that cannot appear in the pattern
or replacement. Characters from the set `"#$&'()*;<=>?`|~' are good
choices if the pattern or replacement might contain a file name, since
they have special meaning to the shell and are less likely to occur in
file names.
*Note Macro Definitions::, for details on how to define a macro. If
a macro doesn't use `AC_REQUIRE', is expected to never be the object of
an `AC_REQUIRE' directive, and macros required by other macros inside
arguments do not need to be expanded before this macro, then use
`m4_define'. In case of doubt, use `AC_DEFUN'. Also take into account
that public third-party macros need to use `AC_DEFUN' in order to be
found by `aclocal' (*note Extending aclocal: (automake)Extending
aclocal.). All the `AC_REQUIRE' statements should be at the beginning
of the macro, and each statement should be followed by `dnl'.
You should not rely on the number of arguments: instead of checking
whether an argument is missing, test that it is not empty. It provides
both a simpler and a more predictable interface to the user, and saves
room for further arguments.
Unless the macro is short, try to leave the closing `])' at the
beginning of a line, followed by a comment that repeats the name of the
macro being defined. This introduces an additional newline in
`configure'; normally, that is not a problem, but if you want to remove
it you can use `[]dnl' on the last line. You can similarly use `[]dnl'
after a macro call to remove its newline. `[]dnl' is recommended
instead of `dnl' to ensure that M4 does not interpret the `dnl' as
being attached to the preceding text or macro output. For example,
instead of:
AC_DEFUN([AC_PATH_X],
[AC_MSG_CHECKING([for X])
AC_REQUIRE_CPP()
# ...omitted...
AC_MSG_RESULT([libraries $x_libraries, headers $x_includes])
fi])
you would write:
AC_DEFUN([AC_PATH_X],
[AC_REQUIRE_CPP()[]dnl
AC_MSG_CHECKING([for X])
# ...omitted...
AC_MSG_RESULT([libraries $x_libraries, headers $x_includes])
fi[]dnl
])# AC_PATH_X
If the macro is long, try to split it into logical chunks.
Typically, macros that check for a bug in a function and prepare its
`AC_LIBOBJ' replacement should have an auxiliary macro to perform this
setup. Do not hesitate to introduce auxiliary macros to factor your
code.
In order to highlight the recommended coding style, here is a macro
written the old way:
dnl Check for EMX on OS/2.
dnl _AC_EMXOS2
AC_DEFUN(_AC_EMXOS2,
[AC_CACHE_CHECK(for EMX OS/2 environment, ac_cv_emxos2,
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, return __EMX__;)],
ac_cv_emxos2=yes, ac_cv_emxos2=no)])
test "x$ac_cv_emxos2" = xyes && EMXOS2=yes])
and the new way:
# _AC_EMXOS2
# ----------
# Check for EMX on OS/2.
m4_define([_AC_EMXOS2],
[AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2],
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])],
[ac_cv_emxos2=yes],
[ac_cv_emxos2=no])])
test "x$ac_cv_emxos2" = xyes && EMXOS2=yes[]dnl
])# _AC_EMXOS2
File: autoconf.info, Node: Portable Shell, Next: Portable Make, Prev: Writing Autoconf Macros, Up: Top
11 Portable Shell Programming
*****************************
When writing your own checks, there are some shell-script programming
techniques you should avoid in order to make your code portable. The
Bourne shell and upward-compatible shells like the Korn shell and Bash
have evolved over the years, and many features added to the original
System7 shell are now supported on all interesting porting targets.
However, the following discussion between Russ Allbery and Robert Lipe
is worth reading:
Russ Allbery:
The GNU assumption that `/bin/sh' is the one and only shell leads
to a permanent deadlock. Vendors don't want to break users'
existing shell scripts, and there are some corner cases in the
Bourne shell that are not completely compatible with a Posix
shell. Thus, vendors who have taken this route will _never_
(OK..."never say never") replace the Bourne shell (as `/bin/sh')
with a Posix shell.
Robert Lipe:
This is exactly the problem. While most (at least most System
V's) do have a Bourne shell that accepts shell functions most
vendor `/bin/sh' programs are not the Posix shell.
So while most modern systems do have a shell _somewhere_ that
meets the Posix standard, the challenge is to find it.
For this reason, part of the job of M4sh (*note Programming in
M4sh::) is to find such a shell. But to prevent trouble, if you're not
using M4sh you should not take advantage of features that were added
after Unix version 7, circa 1977 (*note Systemology::); you should not
use aliases, negated character classes, or even `unset'. `#' comments,
while not in Unix version 7, were retrofitted in the original Bourne
shell and can be assumed to be part of the least common denominator.
On the other hand, if you're using M4sh you can assume that the shell
has the features that were added in SVR2 (circa 1984), including shell
functions, `return', `unset', and I/O redirection for builtins. For
more information, refer to `http://www.in-ulm.de/~mascheck/bourne/'.
However, some pitfalls have to be avoided for portable use of these
constructs; these will be documented in the rest of this chapter. See
in particular *note Shell Functions:: and *note Limitations of Shell
Builtins: Limitations of Builtins.
Some ancient systems have quite small limits on the length of the
`#!' line; for instance, 32 bytes (not including the newline) on SunOS
4. However, these ancient systems are no longer of practical concern.
The set of external programs you should run in a `configure' script
is fairly small. *Note Utilities in Makefiles: (standards)Utilities in
Makefiles, for the list. This restriction allows users to start out
with a fairly small set of programs and build the rest, avoiding too
many interdependencies between packages.
Some of these external utilities have a portable subset of features;
see *note Limitations of Usual Tools::.
There are other sources of documentation about shells. The
specification for the Posix Shell Command Language
(http://www.opengroup.org/susv3/utilities/xcu_chap02.html), though more
generous than the restrictive shell subset described above, is fairly
portable nowadays. Also please see the Shell FAQs
(http://www.faqs.org/faqs/unix-faq/shell/).
* Menu:
* Shellology:: A zoology of shells
* Invoking the Shell:: Invoking the shell as a command
* Here-Documents:: Quirks and tricks
* File Descriptors:: FDs and redirections
* Signal Handling:: Shells, signals, and headaches
* File System Conventions:: File names
* Shell Pattern Matching:: Pattern matching
* Shell Substitutions:: Variable and command expansions
* Assignments:: Varying side effects of assignments
* Parentheses:: Parentheses in shell scripts
* Slashes:: Slashes in shell scripts
* Special Shell Variables:: Variables you should not change
* Shell Functions:: What to look out for if you use them
* Limitations of Builtins:: Portable use of not so portable /bin/sh
* Limitations of Usual Tools:: Portable use of portable tools
File: autoconf.info, Node: Shellology, Next: Invoking the Shell, Up: Portable Shell
11.1 Shellology
===============
There are several families of shells, most prominently the Bourne family
and the C shell family which are deeply incompatible. If you want to
write portable shell scripts, avoid members of the C shell family. The
the Shell difference FAQ
(http://www.faqs.org/faqs/unix-faq/shell/shell-differences/) includes a
small history of Posix shells, and a comparison between several of them.
Below we describe some of the members of the Bourne shell family.
Ash
Ash is often used on GNU/Linux and BSD systems as a light-weight
Bourne-compatible shell. Ash 0.2 has some bugs that are fixed in
the 0.3.x series, but portable shell scripts should work around
them, since version 0.2 is still shipped with many GNU/Linux
distributions.
To be compatible with Ash 0.2:
- don't use `$?' after expanding empty or unset variables, or
at the start of an `eval':
foo=
false
$foo
echo "Do not use it: $?"
false
eval 'echo "Do not use it: $?"'
- don't use command substitution within variable expansion:
cat ${FOO=`bar`}
- beware that single builtin substitutions are not performed by
a subshell, hence their effect applies to the current shell!
*Note Shell Substitutions::, item "Command Substitution".
Bash
To detect whether you are running Bash, test whether
`BASH_VERSION' is set. To require Posix compatibility, run `set
-o posix'. *Note Bash Posix Mode: (bash)Bash POSIX Mode, for
details.
Bash 2.05 and later
Versions 2.05 and later of Bash use a different format for the
output of the `set' builtin, designed to make evaluating its
output easier. However, this output is not compatible with earlier
versions of Bash (or with many other shells, probably). So if you
use Bash 2.05 or higher to execute `configure', you'll need to use
Bash 2.05 for all other build tasks as well.
Ksh
The Korn shell is compatible with the Bourne family and it mostly
conforms to Posix. It has two major variants commonly called
`ksh88' and `ksh93', named after the years of initial release. It
is usually called `ksh', but is called `sh' on some hosts if you
set your path appropriately.
Solaris systems have three variants: `/usr/bin/ksh' is `ksh88'; it
is standard on Solaris 2.0 and later. `/usr/xpg4/bin/sh' is a
Posix-compliant variant of `ksh88'; it is standard on Solaris 9
and later. `/usr/dt/bin/dtksh' is `ksh93'. Variants that are not
standard may be parts of optional packages. There is no extra
charge for these packages, but they are not part of a minimal OS
install and therefore some installations may not have it.
Starting with Tru64 Version 4.0, the Korn shell `/usr/bin/ksh' is
also available as `/usr/bin/posix/sh'. If the environment
variable `BIN_SH' is set to `xpg4', subsidiary invocations of the
standard shell conform to Posix.
Pdksh
A public-domain clone of the Korn shell called `pdksh' is widely
available: it has most of the `ksh88' features along with a few of
its own. It usually sets `KSH_VERSION', except if invoked as
`/bin/sh' on OpenBSD, and similarly to Bash you can require Posix
compatibility by running `set -o posix'. Unfortunately, with
`pdksh' 5.2.14 (the latest stable version as of January 2007)
Posix mode is buggy and causes `pdksh' to depart from Posix in at
least one respect, see *note Shell Substitutions::.
Zsh
To detect whether you are running `zsh', test whether
`ZSH_VERSION' is set. By default `zsh' is _not_ compatible with
the Bourne shell: you must execute `emulate sh', and for `zsh'
versions before 3.1.6-dev-18 you must also set `NULLCMD' to `:'.
*Note Compatibility: (zsh)Compatibility, for details.
The default Mac OS X `sh' was originally Zsh; it was changed to
Bash in Mac OS X 10.2.
File: autoconf.info, Node: Invoking the Shell, Next: Here-Documents, Prev: Shellology, Up: Portable Shell
11.2 Invoking the Shell
=======================
The Korn shell (up to at least version M-12/28/93d) has a bug when
invoked on a file whose name does not contain a slash. It first
searches for the file's name in `PATH', and if found it executes that
rather than the original file. For example, assuming there is a binary
executable `/usr/bin/script' in your `PATH', the last command in the
following example fails because the Korn shell finds `/usr/bin/script'
and refuses to execute it as a shell script:
$ touch xxyzzyz script
$ ksh xxyzzyz
$ ksh ./script
$ ksh script
ksh: script: cannot execute
Bash 2.03 has a bug when invoked with the `-c' option: if the
option-argument ends in backslash-newline, Bash incorrectly reports a
syntax error. The problem does not occur if a character follows the
backslash:
$ $ bash -c 'echo foo \
> '
bash: -c: line 2: syntax error: unexpected end of file
$ bash -c 'echo foo \
> '
foo
*Note Backslash-Newline-Empty::, for how this can cause problems in
makefiles.
File: autoconf.info, Node: Here-Documents, Next: File Descriptors, Prev: Invoking the Shell, Up: Portable Shell
11.3 Here-Documents
===================
Don't rely on `\' being preserved just because it has no special
meaning together with the next symbol. In the native `sh' on OpenBSD
2.7 `\"' expands to `"' in here-documents with unquoted delimiter. As
a general rule, if `\\' expands to `\' use `\\' to get `\'.
With OpenBSD 2.7's `sh'
$ cat < \" \\
> EOF
" \
and with Bash:
bash-2.04$ cat < \" \\
> EOF
\" \
Using command substitutions in a here-document that is fed to a shell
function is not portable. For example, with Solaris 10 `/bin/sh':
$ kitty () { cat; }
$ kitty < `echo ok`
> EOF
/tmp/sh199886: cannot open
$ echo $?
1
Some shells mishandle large here-documents: for example, Solaris 10
`dtksh' and the UnixWare 7.1.1 Posix shell, which are derived from Korn
shell version M-12/28/93d, mishandle braced variable expansion that
crosses a 1024- or 4096-byte buffer boundary within a here-document.
Only the part of the variable name after the boundary is used. For
example, `${variable}' could be replaced by the expansion of `${ble}'.
If the end of the variable name is aligned with the block boundary, the
shell reports an error, as if you used `${}'. Instead of
`${variable-default}', the shell may expand `${riable-default}', or
even `${fault}'. This bug can often be worked around by omitting the
braces: `$variable'. The bug was fixed in `ksh93g' (1998-04-30) but as
of 2006 many operating systems were still shipping older versions with
the bug.
Empty here-documents are not portable either; with the following
code, `zsh' up to at least version 4.3.10 creates a file with a single
newline, whereas other shells create an empty file:
cat >file <; then
assume this and that
else
check this
check that
check something else
...
on and on forever
...
fi
A shell parses the whole `if'/`fi' construct, creating temporary
files for each here-document in it. Some shells create links for such
here-documents on every `fork', so that the clean-up code they had
installed correctly removes them. It is creating the links that can
take the shell forever.
Moving the tests out of the `if'/`fi', or creating multiple
`if'/`fi' constructs, would improve the performance significantly.
Anyway, this kind of construct is not exactly the typical use of
Autoconf. In fact, it's even not recommended, because M4 macros can't
look into shell conditionals, so we may fail to expand a macro when it
was expanded before in a conditional path, and the condition turned out
to be false at runtime, and we end up not executing the macro at all.
Be careful with the use of `<s, and things can
silently break if an overzealous editor converts to using leading
spaces (not all shells are nice enough to warn about unterminated
here-documents).
$ printf 'cat <
File: autoconf.info, Node: File Descriptors, Next: Signal Handling, Prev: Here-Documents, Up: Portable Shell
11.4 File Descriptors
=====================
Most shells, if not all (including Bash, Zsh, Ash), output traces on
stderr, even for subshells. This might result in undesirable content
if you meant to capture the standard-error output of the inner command:
$ ash -x -c '(eval "echo foo >&2") 2>stderr'
$ cat stderr
+ eval echo foo >&2
+ echo foo
foo
$ bash -x -c '(eval "echo foo >&2") 2>stderr'
$ cat stderr
+ eval 'echo foo >&2'
++ echo foo
foo
$ zsh -x -c '(eval "echo foo >&2") 2>stderr'
# Traces on startup files deleted here.
$ cat stderr
+zsh:1> eval echo foo >&2
+zsh:1> echo foo
foo
One workaround is to grep out uninteresting lines, hoping not to remove
good ones.
If you intend to redirect both standard error and standard output,
redirect standard output first. This works better with HP-UX, since
its shell mishandles tracing if standard error is redirected first:
$ sh -x -c ': 2>err >out'
+ :
+ 2> err $ cat err
1> out
Don't try to redirect the standard error of a command substitution.
It must be done _inside_ the command substitution. When running `: `cd
/zorglub` 2>/dev/null' expect the error message to escape, while `: `cd
/zorglub 2>/dev/null`' works properly.
On the other hand, some shells, such as Solaris or FreeBSD
`/bin/sh', warn about missing programs before performing redirections.
Therefore, to silently check whether a program exists, it is necessary
to perform redirections on a subshell or brace group:
$ /bin/sh -c 'nosuch 2>/dev/null'
nosuch: not found
$ /bin/sh -c '(nosuch) 2>/dev/null'
$ /bin/sh -c '{ nosuch; } 2>/dev/null'
$ bash -c 'nosuch 2>/dev/null'
FreeBSD 6.2 sh may mix the trace output lines from the statements in
a shell pipeline.
It is worth noting that Zsh (but not Ash nor Bash) makes it possible
in assignments though: `foo=`cd /zorglub` 2>/dev/null'.
Some shells, like `ash', don't recognize bi-directional redirection
(`<>'). And even on shells that recognize it, it is not portable to
use on fifos: Posix does not require read-write support for named
pipes, and Cygwin does not support it:
$ mkfifo fifo
$ exec 5<>fifo
$ echo hi >&5
bash: echo: write error: Communication error on send
Furthermore, versions of `dash' before 0.5.6 mistakenly truncate
regular files when using `<>':
$ echo a > file
$ bash -c ': 1<>file'; cat file
a
$ dash -c ': 1<>file'; cat file
$ rm a
When catering to old systems, don't redirect the same file descriptor
several times, as you are doomed to failure under Ultrix.
ULTRIX V4.4 (Rev. 69) System #31: Thu Aug 10 19:42:23 GMT 1995
UWS V4.4 (Rev. 11)
$ eval 'echo matter >fullness' >void
illegal io
$ eval '(echo matter >fullness)' >void
illegal io
$ (eval '(echo matter >fullness)') >void
Ambiguous output redirect.
In each case the expected result is of course `fullness' containing
`matter' and `void' being empty. However, this bug is probably not of
practical concern to modern platforms.
Solaris 10 `sh' will try to optimize away a `:' command (even if it
is redirected) in a loop after the first iteration, or in a shell
function after the first call:
$ for i in 1 2 3 ; do : >x$i; done
$ ls x*
x1
$ f () { : >$1; }; f y1; f y2; f y3;
$ ls y*
y1
As a workaround, `echo' or `eval' can be used.
Don't rely on file descriptors 0, 1, and 2 remaining closed in a
subsidiary program. If any of these descriptors is closed, the
operating system may open an unspecified file for the descriptor in the
new process image. Posix 2008 says this may be done only if the
subsidiary program is set-user-ID or set-group-ID, but HP-UX 11.23 does
it even for ordinary programs, and the next version of Posix will allow
HP-UX behavior.
If you want a file descriptor above 2 to be inherited into a child
process, then you must use redirections specific to that command or a
containing subshell or command group, rather than relying on `exec' in
the shell. In `ksh' as well as HP-UX `sh', file descriptors above 2
which are opened using `exec N>file' are closed by a subsequent `exec'
(such as that involved in the fork-and-exec which runs a program or
script):
$ echo 'echo hello >&5' >k
$ /bin/sh -c 'exec 5>t; ksh ./k; exec 5>&-; cat t
hello
$ bash -c 'exec 5>t; ksh ./k; exec 5>&-; cat t
hello
$ ksh -c 'exec 5>t; ksh ./k; exec 5>&-; cat t
./k[1]: 5: cannot open [Bad file number]
$ ksh -c '(ksh ./k) 5>t; cat t'
hello
$ ksh -c '{ ksh ./k; } 5>t; cat t'
hello
$ ksh -c '5>t ksh ./k; cat t
hello
Don't rely on duplicating a closed file descriptor to cause an
error. With Solaris `/bin/sh', failed duplication is silently ignored,
which can cause unintended leaks to the original file descriptor. In
this example, observe the leak to standard output:
$ bash -c 'echo hi >&3' 3>&-; echo $?
bash: 3: Bad file descriptor
1
$ /bin/sh -c 'echo hi >&3' 3>&-; echo $?
hi
0
Fortunately, an attempt to close an already closed file descriptor
will portably succeed. Likewise, it is safe to use either style of
`N&-' for closing a file descriptor, even if it doesn't
match the read/write mode that the file descriptor was opened with.
DOS variants cannot rename or remove open files, such as in `mv foo
bar >foo' or `rm foo >foo', even though this is perfectly portable
among Posix hosts.
A few ancient systems reserved some file descriptors. By convention,
file descriptor 3 was opened to `/dev/tty' when you logged into Eighth
Edition (1985) through Tenth Edition Unix (1989). File descriptor 4
had a special use on the Stardent/Kubota Titan (circa 1990), though we
don't now remember what it was. Both these systems are obsolete, so
it's now safe to treat file descriptors 3 and 4 like any other file
descriptors.
On the other hand, you can't portably use multi-digit file
descriptors. Solaris `ksh' doesn't understand any file descriptor
larger than `9':
$ bash -c 'exec 10>&-'; echo $?
0
$ ksh -c 'exec 9>&-'; echo $?
0
$ ksh -c 'exec 10>&-'; echo $?
ksh[1]: exec: 10: not found
127
File: autoconf.info, Node: Signal Handling, Next: File System Conventions, Prev: File Descriptors, Up: Portable Shell
11.5 Signal Handling
====================
Portable handling of signals within the shell is another major source of
headaches. This is worsened by the fact that various different,
mutually incompatible approaches are possible in this area, each with
its distinctive merits and demerits. A detailed description of these
possible approaches, as well as of their pros and cons, can be found in
this article (http://www.cons.org/cracauer/sigint.html).
Solaris 10 `/bin/sh' automatically traps most signals by default;
the shell still exits with error upon termination by one of those
signals, but in such a case the exit status might be somewhat
unexpected (even if allowed by POSIX, strictly speaking):
$ bash -c 'kill -1 $$'; echo $? # Will exit 128 + (signal number).
Hangup
129
$ /bin/ksh -c 'kill -15 $$'; echo $? # Likewise.
Terminated
143
$ for sig in 1 2 3 15; do
> echo $sig:
> /bin/sh -c "kill -$s \$\$"; echo $?
> done
signal 1:
Hangup
129
signal 2:
208
signal 3:
208
signal 15:
208
This gets even worse if one is using the POSIX `wait' interface to
get details about the shell process terminations: it will result in the
shell having exited normally, rather than by receiving a signal.
$ cat > foo.c < /* for printf */
#include /* for system */
#include /* for WIF* macros */
int main(void)
{
int status = system ("kill -15 $$");
printf ("Terminated by signal: %s\n",
WIFSIGNALED (status) ? "yes" : "no");
printf ("Exited normally: %s\n",
WIFEXITED (status) ? "yes" : "no");
return 0;
}
END
$ cc -o foo foo.c
$ ./a.out # On GNU/Linux
Terminated by signal: no
Exited normally: yes
$ ./a.out # On Solaris 10
Terminated by signal: yes
Exited normally: no
Various shells seem to handle `SIGQUIT' specially: they ignore it
even if it is not blocked, and even if the shell is not running
interactively (in fact, even if the shell has no attached tty); among
these shells are at least Bash (from version 2 onwards), Zsh 4.3.12,
Solaris 10 `/bin/ksh' and `/usr/xpg4/bin/sh', and AT&T `ksh93' (2011).
Still, `SIGQUIT' seems to be trappable quite portably within all these
shells. OTOH, some other shells doesn't special-case the handling of
`SIGQUIT'; among these shells are at least `pdksh' 5.2.14, Solaris 10
and NetBSD 5.1 `/bin/sh', and the Almquist Shell 0.5.5.1.
Some shells (especially Korn shells and derivatives) might try to
propagate to themselves a signal that has killed a child process; this
is not a bug, but a conscious design choice (although its overall value
might be debatable). The exact details of how this is attained vary
from shell to shell. For example, upon running `perl -e 'kill 2, $$'',
after the perl process has been interrupted AT&T `ksh93' (2011) will
proceed to send itself a `SIGINT', while Solaris 10 `/bin/ksh' and
`/usr/xpg4/bin/sh' will proceed to exit with status 130 (i.e., 128 +
2). In any case, if there is an active trap associated with `SIGINT',
those shells will correctly execute it.
Some Korn shells, when a child process die due receiving a signal
with signal number N, can leave in `$?' an exit status of 256+N instead
of the more common 128+N. Observe the difference between AT&T `ksh93'
(2011) and `bash' 4.1.5 on Debian:
$ /bin/ksh -c 'sh -c "kill -1 \$\$"; echo $?'
/bin/ksh: line 1: 7837: Hangup
257
$ /bin/bash -c 'sh -c "kill -1 \$\$"; echo $?'
/bin/bash: line 1: 7861 Hangup (sh -c "kill -1 \$\$")
129
This `ksh' behavior is allowed by POSIX, if implemented with due care;
see this Austin Group discussion
(http://www.austingroupbugs.net/view.php?id=51) for more background.
However, if it is not implemented with proper care, such a behavior
might cause problems in some corner cases. To see why, assume we have
a "wrapper" script like this:
#!/bin/sh
# Ignore some signals in the shell only, not in its child processes.
trap : 1 2 13 15
wrapped_command "$@"
ret=$?
other_command
exit $ret
If `wrapped_command' is interrupted by a `SIGHUP' (which has signal
number 1), `ret' will be set to 257. Unless the `exit' shell builtin
is smart enough to understand that such a value can only have
originated from a signal, and adjust the final wait status of the shell
appropriately, the value 257 will just get truncated to 1 by the
closing `exit' call, so that a caller of the script will have no way to
determine that termination by a signal was involved. Observe the
different behavior of AT&T `ksh93' (2011) and `bash' 4.1.5 on Debian:
$ cat foo.sh
#!/bin/sh
sh -c 'kill -1 $$'
ret=$?
echo $ret
exit $ret
$ /bin/ksh foo.sh; echo $?
foo.sh: line 2: 12479: Hangup
257
1
$ /bin/bash foo.sh; echo $?
foo.sh: line 2: 12487 Hangup (sh -c 'kill -1 $$')
129
129
File: autoconf.info, Node: File System Conventions, Next: Shell Pattern Matching, Prev: Signal Handling, Up: Portable Shell
11.6 File System Conventions
============================
Autoconf uses shell-script processing extensively, so the file names
that it processes should not contain characters that are special to the
shell. Special characters include space, tab, newline, NUL, and the
following:
" # $ & ' ( ) * ; < = > ? [ \ ` |
Also, file names should not begin with `~' or `-', and should
contain neither `-' immediately after `/' nor `~' immediately after
`:'. On Posix-like platforms, directory names should not contain `:',
as this runs afoul of `:' used as the path separator.
These restrictions apply not only to the files that you distribute,
but also to the absolute file names of your source, build, and
destination directories.
On some Posix-like platforms, `!' and `^' are special too, so they
should be avoided.
Posix lets implementations treat leading `//' specially, but
requires leading `///' and beyond to be equivalent to `/'. Most Unix
variants treat `//' like `/'. However, some treat `//' as a
"super-root" that can provide access to files that are not otherwise
reachable from `/'. The super-root tradition began with Apollo
Domain/OS, which died out long ago, but unfortunately Cygwin has
revived it.
While `autoconf' and friends are usually run on some Posix variety,
they can be used on other systems, most notably DOS variants. This
impacts several assumptions regarding file names.
For example, the following code:
case $foo_dir in
/*) # Absolute
;;
*)
foo_dir=$dots$foo_dir ;;
esac
fails to properly detect absolute file names on those systems, because
they can use a drivespec, and usually use a backslash as directory
separator. If you want to be portable to DOS variants (at the price of
rejecting valid but oddball Posix file names like `a:\b'), you can
check for absolute file names like this:
case $foo_dir in
[\\/]* | ?:[\\/]* ) # Absolute
;;
*)
foo_dir=$dots$foo_dir ;;
esac
Make sure you quote the brackets if appropriate and keep the backslash
as first character (*note Limitations of Shell Builtins: case.).
Also, because the colon is used as part of a drivespec, these
systems don't use it as path separator. When creating or accessing
paths, you can use the `PATH_SEPARATOR' output variable instead.
`configure' sets this to the appropriate value for the build system
(`:' or `;') when it starts up.
File names need extra care as well. While DOS variants that are
Posixy enough to run `autoconf' (such as DJGPP) are usually able to
handle long file names properly, there are still limitations that can
seriously break packages. Several of these issues can be easily
detected by the doschk
(ftp://ftp.gnu.org/gnu/non-gnu/doschk/doschk-1.1.tar.gz) package.
A short overview follows; problems are marked with SFN/LFN to
indicate where they apply: SFN means the issues are only relevant to
plain DOS, not to DOS under Microsoft Windows variants, while LFN
identifies problems that exist even under Microsoft Windows variants.
No multiple dots (SFN)
DOS cannot handle multiple dots in file names. This is an
especially important thing to remember when building a portable
configure script, as `autoconf' uses a .in suffix for template
files.
This is perfectly OK on Posix variants:
AC_CONFIG_HEADERS([config.h])
AC_CONFIG_FILES([source.c foo.bar])
AC_OUTPUT
but it causes problems on DOS, as it requires `config.h.in',
`source.c.in' and `foo.bar.in'. To make your package more portable
to DOS-based environments, you should use this instead:
AC_CONFIG_HEADERS([config.h:config.hin])
AC_CONFIG_FILES([source.c:source.cin foo.bar:foobar.in])
AC_OUTPUT
No leading dot (SFN)
DOS cannot handle file names that start with a dot. This is
usually not important for `autoconf'.
Case insensitivity (LFN)
DOS is case insensitive, so you cannot, for example, have both a
file called `INSTALL' and a directory called `install'. This also
affects `make'; if there's a file called `INSTALL' in the
directory, `make install' does nothing (unless the `install'
target is marked as PHONY).
The 8+3 limit (SFN)
Because the DOS file system only stores the first 8 characters of
the file name and the first 3 of the extension, those must be
unique. That means that `foobar-part1.c', `foobar-part2.c' and
`foobar-prettybird.c' all resolve to the same file name
(`FOOBAR-P.C'). The same goes for `foo.bar' and `foo.bartender'.
The 8+3 limit is not usually a problem under Microsoft Windows, as
it uses numeric tails in the short version of file names to make
them unique. However, a registry setting can turn this behavior
off. While this makes it possible to share file trees containing
long file names between SFN and LFN environments, it also means
the above problem applies there as well.
Invalid characters (LFN)
Some characters are invalid in DOS file names, and should therefore
be avoided. In a LFN environment, these are `/', `\', `?', `*',
`:', `', `|' and `"'. In a SFN environment, other
characters are also invalid. These include `+', `,', `[' and `]'.
Invalid names (LFN)
Some DOS file names are reserved, and cause problems if you try to
use files with those names. These names include `CON', `AUX',
`COM1', `COM2', `COM3', `COM4', `LPT1', `LPT2', `LPT3', `NUL', and
`PRN'. File names are case insensitive, so even names like
`aux/config.guess' are disallowed.
File: autoconf.info, Node: Shell Pattern Matching, Next: Shell Substitutions, Prev: File System Conventions, Up: Portable Shell
11.7 Shell Pattern Matching
===========================
Nowadays portable patterns can use negated character classes like
`[!-aeiou]'. The older syntax `[^-aeiou]' is supported by some shells
but not others; hence portable scripts should never use `^' as the
first character of a bracket pattern.
Outside the C locale, patterns like `[a-z]' are problematic since
they may match characters that are not lower-case letters.
File: autoconf.info, Node: Shell Substitutions, Next: Assignments, Prev: Shell Pattern Matching, Up: Portable Shell
11.8 Shell Substitutions
========================
Contrary to a persistent urban legend, the Bourne shell does not
systematically split variables and back-quoted expressions, in
particular on the right-hand side of assignments and in the argument of
`case'. For instance, the following code:
case "$given_srcdir" in
.) top_srcdir="`echo "$dots" | sed 's|/$||'`" ;;
*) top_srcdir="$dots$given_srcdir" ;;
esac
is more readable when written as:
case $given_srcdir in
.) top_srcdir=`echo "$dots" | sed 's|/$||'` ;;
*) top_srcdir=$dots$given_srcdir ;;
esac
and in fact it is even _more_ portable: in the first case of the first
attempt, the computation of `top_srcdir' is not portable, since not all
shells properly understand `"`..."..."...`"', for example Solaris 10
ksh:
$ foo="`echo " bar" | sed 's, ,,'`"
ksh: : cannot execute
ksh: bar | sed 's, ,,': cannot execute
Posix does not specify behavior for this sequence. On the other hand,
behavior for `"`...\"...\"...`"' is specified by Posix, but in
practice, not all shells understand it the same way: pdksh 5.2.14
prints spurious quotes when in Posix mode:
$ echo "`echo \"hello\"`"
hello
$ set -o posix
$ echo "`echo \"hello\"`"
"hello"
There is just no portable way to use double-quoted strings inside
double-quoted back-quoted expressions (pfew!).
Bash 4.1 has a bug where quoted empty strings adjacent to unquoted
parameter expansions are elided during word splitting. Meanwhile, zsh
does not perform word splitting except when in Bourne compatibility
mode. In the example below, the correct behavior is to have five
arguments to the function, and exactly two spaces on either side of the
middle `-', since word splitting collapses multiple spaces in `$f' but
leaves empty arguments intact.
$ bash -c 'n() { echo "$#$@"; }; f=" - "; n - ""$f"" -'
3- - -
$ ksh -c 'n() { echo "$#$@"; }; f=" - "; n - ""$f"" -'
5- - -
$ zsh -c 'n() { echo "$#$@"; }; f=" - "; n - ""$f"" -'
3- - -
$ zsh -c 'emulate sh;
> n() { echo "$#$@"; }; f=" - "; n - ""$f"" -'
5- - -
You can work around this by doing manual word splitting, such as using
`"$str" $list' rather than `"$str"$list'.
There are also portability pitfalls with particular expansions:
`$@'
One of the most famous shell-portability issues is related to
`"$@"'. When there are no positional arguments, Posix says that
`"$@"' is supposed to be equivalent to nothing, but the original
Unix version 7 Bourne shell treated it as equivalent to `""'
instead, and this behavior survives in later implementations like
Digital Unix 5.0.
The traditional way to work around this portability problem is to
use `${1+"$@"}'. Unfortunately this method does not work with Zsh
(3.x and 4.x), which is used on Mac OS X. When emulating the
Bourne shell, Zsh performs word splitting on `${1+"$@"}':
zsh $ emulate sh
zsh $ for i in "$@"; do echo $i; done
Hello World
!
zsh $ for i in ${1+"$@"}; do echo $i; done
Hello
World
!
Zsh handles plain `"$@"' properly, but we can't use plain `"$@"'
because of the portability problems mentioned above. One
workaround relies on Zsh's "global aliases" to convert `${1+"$@"}'
into `"$@"' by itself:
test "${ZSH_VERSION+set}" = set && alias -g '${1+"$@"}'='"$@"'
Zsh only recognizes this alias when a shell word matches it
exactly; `"foo"${1+"$@"}' remains subject to word splitting.
Since this case always yields at least one shell word, use plain
`"$@"'.
A more conservative workaround is to avoid `"$@"' if it is
possible that there may be no positional arguments. For example,
instead of:
cat conftest.c "$@"
you can use this instead:
case $# in
0) cat conftest.c;;
*) cat conftest.c "$@";;
esac
Autoconf macros often use the `set' command to update `$@', so if
you are writing shell code intended for `configure' you should not
assume that the value of `$@' persists for any length of time.
`${10}'
The 10th, 11th, ... positional parameters can be accessed only
after a `shift'. The 7th Edition shell reported an error if given
`${10}', and Solaris 10 `/bin/sh' still acts that way:
$ set 1 2 3 4 5 6 7 8 9 10
$ echo ${10}
bad substitution
Conversely, not all shells obey the Posix rule that when braces are
omitted, multiple digits beyond a `$' imply the single-digit
positional parameter expansion concatenated with the remaining
literal digits. To work around the issue, you must use braces.
$ bash -c 'set a b c d e f g h i j; echo $10 ${1}0'
a0 a0
$ dash -c 'set a b c d e f g h i j; echo $10 ${1}0'
j a0
`${VAR:-VALUE}'
Old BSD shells, including the Ultrix `sh', don't accept the colon
for any shell substitution, and complain and die. Similarly for
${VAR:=VALUE}, ${VAR:?VALUE}, etc. However, all shells that
support functions allow the use of colon in shell substitution,
and since m4sh requires functions, you can portably use null
variable substitution patterns in configure scripts.
`${VAR+VALUE}'
When using `${VAR-VALUE}' or `${VAR-VALUE}' for providing
alternate substitutions, VALUE must either be a single shell word,
quoted, or in the context of an unquoted here-document. Solaris
`/bin/sh' complains otherwise.
$ /bin/sh -c 'echo ${a-b c}'
/bin/sh: bad substitution
$ /bin/sh -c 'echo ${a-'\''b c'\''}'
b c
$ /bin/sh -c 'echo "${a-b c}"'
b c
$ /bin/sh -c 'cat < broken
$ echo "`printf 'foo\r\n'`"" bar" | cmp - broken
- broken differ: char 4, line 1
Upon interrupt or SIGTERM, some shells may abort a command
substitution, replace it with a null string, and wrongly evaluate
the enclosing command before entering the trap or ending the
script. This can lead to spurious errors:
$ sh -c 'if test `sleep 5; echo hi` = hi; then echo yes; fi'
$ ^C
sh: test: hi: unexpected operator/operand
You can avoid this by assigning the command substitution to a
temporary variable:
$ sh -c 'res=`sleep 5; echo hi`
if test "x$res" = xhi; then echo yes; fi'
$ ^C
`$(COMMANDS)'
This construct is meant to replace ``COMMANDS`', and it has most
of the problems listed under ``COMMANDS`'.
This construct can be nested while this is impossible to do
portably with back quotes. Unfortunately it is not yet
universally supported. Most notably, even recent releases of
Solaris don't support it:
$ showrev -c /bin/sh | grep version
Command version: SunOS 5.10 Generic 121005-03 Oct 2006
$ echo $(echo blah)
syntax error: `(' unexpected
nor does IRIX 6.5's Bourne shell:
$ uname -a
IRIX firebird-image 6.5 07151432 IP22
$ echo $(echo blah)
$(echo blah)
If you do use `$(COMMANDS)', make sure that the commands do not
start with a parenthesis, as that would cause confusion with a
different notation `$((EXPRESSION))' that in modern shells is an
arithmetic expression not a command. To avoid the confusion,
insert a space between the two opening parentheses.
Avoid COMMANDS that contain unbalanced parentheses in
here-documents, comments, or case statement patterns, as many
shells mishandle them. For example, Bash 3.1, `ksh88', `pdksh'
5.2.14, and Zsh 4.2.6 all mishandle the following valid command:
echo $(case x in x) echo hello;; esac)
`$((EXPRESSION))'
Arithmetic expansion is not portable as some shells (most notably
Solaris 10 `/bin/sh') don't support it.
Among shells that do support `$(( ))', not all of them obey the
Posix rule that octal and hexadecimal constants must be recognized:
$ bash -c 'echo $(( 010 + 0x10 ))'
24
$ zsh -c 'echo $(( 010 + 0x10 ))'
26
$ zsh -c 'emulate sh; echo $(( 010 + 0x10 ))'
24
$ pdksh -c 'echo $(( 010 + 0x10 ))'
pdksh: 010 + 0x10 : bad number `0x10'
$ pdksh -c 'echo $(( 010 ))'
10
When it is available, using arithmetic expansion provides a
noticeable speedup in script execution; but testing for support
requires `eval' to avoid syntax errors. The following construct
is used by `AS_VAR_ARITH' to provide arithmetic computation when
all arguments are provided in decimal and without a leading zero,
and all operators are properly quoted and appear as distinct
arguments:
if ( eval 'test $(( 1 + 1 )) = 2' ) 2>/dev/null; then
eval 'func_arith ()
{
func_arith_result=$(( $* ))
}'
else
func_arith ()
{
func_arith_result=`expr "$@"`
}
fi
func_arith 1 + 1
foo=$func_arith_result
`^'
Always quote `^', otherwise traditional shells such as `/bin/sh'
on Solaris 10 treat this like `|'.
File: autoconf.info, Node: Assignments, Next: Parentheses, Prev: Shell Substitutions, Up: Portable Shell
11.9 Assignments
================
When setting several variables in a row, be aware that the order of the
evaluation is undefined. For instance `foo=1 foo=2; echo $foo' gives
`1' with Solaris `/bin/sh', but `2' with Bash. You must use `;' to
enforce the order: `foo=1; foo=2; echo $foo'.
Don't rely on the following to find `subdir/program':
PATH=subdir$PATH_SEPARATOR$PATH program
as this does not work with Zsh 3.0.6. Use something like this instead:
(PATH=subdir$PATH_SEPARATOR$PATH; export PATH; exec program)
Don't rely on the exit status of an assignment: Ash 0.2 does not
change the status and propagates that of the last statement:
$ false || foo=bar; echo $?
1
$ false || foo=`:`; echo $?
0
and to make things even worse, QNX 4.25 just sets the exit status to 0
in any case:
$ foo=`exit 1`; echo $?
0
To assign default values, follow this algorithm:
1. If the default value is a literal and does not contain any closing
brace, use:
: "${var='my literal'}"
2. If the default value contains no closing brace, has to be
expanded, and the variable being initialized is not intended to be
IFS-split (i.e., it's not a list), then use:
: ${var="$default"}
3. If the default value contains no closing brace, has to be
expanded, and the variable being initialized is intended to be
IFS-split (i.e., it's a list), then use:
var=${var="$default"}
4. If the default value contains a closing brace, then use:
test "${var+set}" = set || var="has a '}'"
In most cases `var=${var="$default"}' is fine, but in case of doubt,
just use the last form. *Note Shell Substitutions::, items
`${VAR:-VALUE}' and `${VAR=VALUE}' for the rationale.
File: autoconf.info, Node: Parentheses, Next: Slashes, Prev: Assignments, Up: Portable Shell
11.10 Parentheses in Shell Scripts
==================================
Beware of two opening parentheses in a row, as many shell
implementations treat them specially, and Posix says that a portable
script cannot use `((' outside the `$((' form used for shell
arithmetic. In traditional shells, `((cat))' behaves like `(cat)'; but
many shells, including Bash and the Korn shell, treat `((cat))' as an
arithmetic expression equivalent to `let "cat"', and may or may not
report an error when they detect that `cat' is not a number. As another
example, `pdksh' 5.2.14 does not treat the following code as a
traditional shell would:
if ((true) || false); then
echo ok
fi
To work around this problem, insert a space between the two opening
parentheses. There is a similar problem and workaround with `$(('; see
*note Shell Substitutions::.
File: autoconf.info, Node: Slashes, Next: Special Shell Variables, Prev: Parentheses, Up: Portable Shell
11.11 Slashes in Shell Scripts
==============================
Unpatched Tru64 5.1 `sh' omits the last slash of command-line arguments
that contain two trailing slashes:
$ echo / // /// //// .// //.
/ / // /// ./ //.
$ x=//
$ eval "echo \$x"
/
$ set -x
$ echo abc | tr -t ab //
+ echo abc
+ tr -t ab /
/bc
Unpatched Tru64 4.0 `sh' adds a slash after `"$var"' if the variable
is empty and the second double-quote is followed by a word that begins
and ends with slash:
$ sh -xc 'p=; echo "$p"/ouch/'
p=
+ echo //ouch/
//ouch/
However, our understanding is that patches are available, so perhaps
it's not worth worrying about working around these horrendous bugs.
File: autoconf.info, Node: Special Shell Variables, Next: Shell Functions, Prev: Slashes, Up: Portable Shell
11.12 Special Shell Variables
=============================
Some shell variables should not be used, since they can have a deep
influence on the behavior of the shell. In order to recover a sane
behavior from the shell, some variables should be unset; M4sh takes
care of this and provides fallback values, whenever needed, to cater
for a very old `/bin/sh' that does not support `unset'. (*note
Portable Shell Programming: Portable Shell.).
As a general rule, shell variable names containing a lower-case
letter are safe; you can define and use these variables without
worrying about their effect on the underlying system, and without
worrying about whether the shell changes them unexpectedly. (The
exception is the shell variable `status', as described below.)
Here is a list of names that are known to cause trouble. This list
is not exhaustive, but you should be safe if you avoid the name
`status' and names containing only upper-case letters and underscores.
`?'
Not all shells correctly reset `$?' after conditionals (*note
Limitations of Shell Builtins: if.). Not all shells manage `$?'
correctly in shell functions (*note Shell Functions::) or in traps
(*note Limitations of Shell Builtins: trap.). Not all shells reset
`$?' to zero after an empty command.
$ bash -c 'false; $empty; echo $?'
0
$ zsh -c 'false; $empty; echo $?'
1
`_'
Many shells reserve `$_' for various purposes, e.g., the name of
the last command executed.
`BIN_SH'
In Tru64, if `BIN_SH' is set to `xpg4', subsidiary invocations of
the standard shell conform to Posix.
`CDPATH'
When this variable is set it specifies a list of directories to
search when invoking `cd' with a relative file name that did not
start with `./' or `../'. Posix 1003.1-2001 says that if a
nonempty directory name from `CDPATH' is used successfully, `cd'
prints the resulting absolute file name. Unfortunately this
output can break idioms like `abs=`cd src && pwd`' because `abs'
receives the name twice. Also, many shells do not conform to this
part of Posix; for example, `zsh' prints the result only if a
directory name other than `.' was chosen from `CDPATH'.
In practice the shells that have this problem also support
`unset', so you can work around the problem as follows:
(unset CDPATH) >/dev/null 2>&1 && unset CDPATH
You can also avoid output by ensuring that your directory name is
absolute or anchored at `./', as in `abs=`cd ./src && pwd`'.
Configure scripts use M4sh, which automatically unsets `CDPATH' if
possible, so you need not worry about this problem in those
scripts.
`CLICOLOR_FORCE'
When this variable is set, some implementations of tools like `ls'
attempt to add color to their output via terminal escape
sequences, even when the output is not directed to a terminal, and
can thus cause spurious failures in scripts. Configure scripts
use M4sh, which automatically unsets this variable.
`DUALCASE'
In the MKS shell, case statements and file name generation are
case-insensitive unless `DUALCASE' is nonzero. Autoconf-generated
scripts export this variable when they start up.
`ENV'
`MAIL'
`MAILPATH'
`PS1'
`PS2'
`PS4'
These variables should not matter for shell scripts, since they are
supposed to affect only interactive shells. However, at least one
shell (the pre-3.0 UWIN Korn shell) gets confused about whether it
is interactive, which means that (for example) a `PS1' with a side
effect can unexpectedly modify `$?'. To work around this bug,
M4sh scripts (including `configure' scripts) do something like
this:
(unset ENV) >/dev/null 2>&1 && unset ENV MAIL MAILPATH
PS1='$ '
PS2='> '
PS4='+ '
(actually, there is some complication due to bugs in `unset';
*note Limitations of Shell Builtins: unset.).
`FPATH'
The Korn shell uses `FPATH' to find shell functions, so avoid
`FPATH' in portable scripts. `FPATH' is consulted after `PATH',
but you still need to be wary of tests that use `PATH' to find
whether a command exists, since they might report the wrong result
if `FPATH' is also set.
`GREP_OPTIONS'
When this variable is set, some implementations of `grep' honor
these options, even if the options include direction to enable
colored output via terminal escape sequences, and the result can
cause spurious failures when the output is not directed to a
terminal. Configure scripts use M4sh, which automatically unsets
this variable.
`IFS'
Long ago, shell scripts inherited `IFS' from the environment, but
this caused many problems so modern shells ignore any environment
settings for `IFS'.
Don't set the first character of `IFS' to backslash. Indeed,
Bourne shells use the first character (backslash) when joining the
components in `"$@"' and some shells then reinterpret (!) the
backslash escapes, so you can end up with backspace and other
strange characters.
The proper value for `IFS' (in regular code, not when performing
splits) is `'. The first character is especially
important, as it is used to join the arguments in `$*'; however,
note that traditional shells, but also bash-2.04, fail to adhere
to this and join with a space anyway.
M4sh guarantees that `IFS' will have the default value at the
beginning of a script, and many macros within autoconf rely on this
setting. It is okay to use blocks of shell code that temporarily
change the value of `IFS' in order to split on another character,
but remember to restore it before expanding further macros.
Unsetting `IFS' instead of resetting it to the default sequence is
not suggested, since code that tries to save and restore the
variable's value will incorrectly reset it to an empty value, thus
disabling field splitting:
unset IFS
# default separators used for field splitting
save_IFS=$IFS
IFS=:
# ...
IFS=$save_IFS
# no field splitting performed
`LANG'
`LC_ALL'
`LC_COLLATE'
`LC_CTYPE'
`LC_MESSAGES'
`LC_MONETARY'
`LC_NUMERIC'
`LC_TIME'
You should set all these variables to `C' because so much
configuration code assumes the C locale and Posix requires that
locale environment variables be set to `C' if the C locale is
desired; `configure' scripts and M4sh do that for you. Export
these variables after setting them.
`LANGUAGE'
`LANGUAGE' is not specified by Posix, but it is a GNU extension
that overrides `LC_ALL' in some cases, so you (or M4sh) should set
it too.
`LC_ADDRESS'
`LC_IDENTIFICATION'
`LC_MEASUREMENT'
`LC_NAME'
`LC_PAPER'
`LC_TELEPHONE'
These locale environment variables are GNU extensions. They are
treated like their Posix brethren (`LC_COLLATE', etc.) as
described above.
`LINENO'
Most modern shells provide the current line number in `LINENO'.
Its value is the line number of the beginning of the current
command. M4sh, and hence Autoconf, attempts to execute
`configure' with a shell that supports `LINENO'. If no such shell
is available, it attempts to implement `LINENO' with a Sed prepass
that replaces each instance of the string `$LINENO' (not followed
by an alphanumeric character) with the line's number. In M4sh
scripts you should execute `AS_LINENO_PREPARE' so that these
workarounds are included in your script; configure scripts do this
automatically in `AC_INIT'.
You should not rely on `LINENO' within `eval' or shell functions,
as the behavior differs in practice. The presence of a quoted
newline within simple commands can alter which line number is used
as the starting point for `$LINENO' substitutions within that
command. Also, the possibility of the Sed prepass means that you
should not rely on `$LINENO' when quoted, when in here-documents,
or when line continuations are used. Subshells should be OK,
though. In the following example, lines 1, 9, and 14 are
portable, but the other instances of `$LINENO' do not have
deterministic values:
$ cat lineno
echo 1. $LINENO
echo "2. $LINENO
3. $LINENO"
cat < sed '
> N
> s,$,-,
> t loop
> :loop
> s,^\([0-9]*\)\(.*\)[$]LINENO\([^a-zA-Z0-9_]\),\1\2\1\3,
> t loop
> s,-$,,
> s,^[0-9]*\n,,
> ' |
> sh
1. 1
2. 2
3. 3
5. 5
6. 6
7. \7
9. 9
10. 10
11. 11
12. 12
13. 13
14. 14
15. 15
18. 16
18. 17
19. 20
In particular, note that `config.status' (and any other subsidiary
script created by `AS_INIT_GENERATED') might report line numbers
relative to the parent script as a result of the potential Sed
pass.
`NULLCMD'
When executing the command `>foo', `zsh' executes `$NULLCMD >foo'
unless it is operating in Bourne shell compatibility mode and the
`zsh' version is newer than 3.1.6-dev-18. If you are using an
older `zsh' and forget to set `NULLCMD', your script might be
suspended waiting for data on its standard input.
`options'
For `zsh' 4.3.10, `options' is treated as an associative array
even after `emulate sh', so it should not be used.
`PATH_SEPARATOR'
On DJGPP systems, the `PATH_SEPARATOR' environment variable can be
set to either `:' or `;' to control the path separator Bash uses
to set up certain environment variables (such as `PATH'). You can
set this variable to `;' if you want `configure' to use `;' as a
separator; this might be useful if you plan to use non-Posix
shells to execute files. *Note File System Conventions::, for
more information about `PATH_SEPARATOR'.
`POSIXLY_CORRECT'
In the GNU environment, exporting `POSIXLY_CORRECT' with any value
(even empty) causes programs to try harder to conform to Posix.
Autoconf does not directly manipulate this variable, but `bash'
ties the shell variable `POSIXLY_CORRECT' to whether the script is
running in Posix mode. Therefore, take care when exporting or
unsetting this variable, so as not to change whether `bash' is in
Posix mode.
$ bash --posix -c 'set -o | grep posix
> unset POSIXLY_CORRECT
> set -o | grep posix'
posix on
posix off
`PWD'
Posix 1003.1-2001 requires that `cd' and `pwd' must update the
`PWD' environment variable to point to the logical name of the
current directory, but traditional shells do not support this.
This can cause confusion if one shell instance maintains `PWD' but
a subsidiary and different shell does not know about `PWD' and
executes `cd'; in this case `PWD' points to the wrong directory.
Use ``pwd`' rather than `$PWD'.
`RANDOM'
Many shells provide `RANDOM', a variable that returns a different
integer each time it is used. Most of the time, its value does not
change when it is not used, but on IRIX 6.5 the value changes all
the time. This can be observed by using `set'. It is common
practice to use `$RANDOM' as part of a file name, but code
shouldn't rely on `$RANDOM' expanding to a nonempty string.
`status'
This variable is an alias to `$?' for `zsh' (at least 3.1.6),
hence read-only. Do not use it.
File: autoconf.info, Node: Shell Functions, Next: Limitations of Builtins, Prev: Special Shell Variables, Up: Portable Shell
11.13 Shell Functions
=====================
Nowadays, it is difficult to find a shell that does not support shell
functions at all. However, some differences should be expected.
When declaring a shell function, you must include whitespace between
the `)' after the function name and the start of the compound
expression, to avoid upsetting `ksh'. While it is possible to use any
compound command, most scripts use `{...}'.
$ /bin/sh -c 'a(){ echo hi;}; a'
hi
$ ksh -c 'a(){ echo hi;}; a'
ksh: syntax error at line 1: `}' unexpected
$ ksh -c 'a() { echo hi;}; a'
hi
Inside a shell function, you should not rely on the error status of a
subshell if the last command of that subshell was `exit' or `trap', as
this triggers bugs in zsh 4.x; while Autoconf tries to find a shell
that does not exhibit the bug, zsh might be the only shell present on
the user's machine.
Likewise, the state of `$?' is not reliable when entering a shell
function. This has the effect that using a function as the first
command in a `trap' handler can cause problems.
$ bash -c 'foo() { echo $?; }; trap foo 0; (exit 2); exit 2'; echo $?
2
2
$ ash -c 'foo() { echo $?; }; trap foo 0; (exit 2); exit 2'; echo $?
0
2
DJGPP bash 2.04 has a bug in that `return' from a shell function
which also used a command substitution causes a segmentation fault. To
work around the issue, you can use `return' from a subshell, or
`AS_SET_STATUS' as last command in the execution flow of the function
(*note Common Shell Constructs::).
Not all shells treat shell functions as simple commands impacted by
`set -e', for example with Solaris 10 `/bin/sh':
$ bash -c 'f() { return 1; }; set -e; f; echo oops'
$ /bin/sh -c 'f() { return 1; }; set -e; f; echo oops'
oops
Shell variables and functions may share the same namespace, for
example with Solaris 10 `/bin/sh':
$ f () { :; }; f=; f
f: not found
For this reason, Autoconf (actually M4sh, *note Programming in M4sh::)
uses the prefix `as_fn_' for its functions.
Handling of positional parameters and shell options varies among
shells. For example, Korn shells reset and restore trace output (`set
-x') and other options upon function entry and exit. Inside a function,
IRIX sh sets `$0' to the function name.
It is not portable to pass temporary environment variables to shell
functions. Solaris `/bin/sh' does not see the variable. Meanwhile,
not all shells follow the Posix rule that the assignment must affect
the current environment in the same manner as special built-ins.
$ /bin/sh -c 'func() { echo $a;}; a=1 func; echo $a'
=>
=>
$ ash -c 'func() { echo $a;}; a=1 func; echo $a'
=>1
=>
$ bash -c 'set -o posix; func() { echo $a;}; a=1 func; echo $a'
=>1
=>1
Some ancient Bourne shell variants with function support did not
reset `$I, I >= 0', upon function exit, so effectively the arguments of
the script were lost after the first function invocation. It is
probably not worth worrying about these shells any more.
With AIX sh, a `trap' on 0 installed in a shell function triggers at
function exit rather than at script exit. *Note Limitations of Shell
Builtins: trap.
File: autoconf.info, Node: Limitations of Builtins, Next: Limitations of Usual Tools, Prev: Shell Functions, Up: Portable Shell
11.14 Limitations of Shell Builtins
===================================
No, no, we are serious: some shells do have limitations! :)
You should always keep in mind that any builtin or command may
support options, and therefore differ in behavior with arguments
starting with a dash. For instance, even the innocent `echo "$word"'
can give unexpected results when `word' starts with a dash. It is
often possible to avoid this problem using `echo "x$word"', taking the
`x' into account later in the pipe. Many of these limitations can be
worked around using M4sh (*note Programming in M4sh::).
`.'
Use `.' only with regular files (use `test -f'). Bash 2.03, for
instance, chokes on `. /dev/null'. Remember that `.' uses `PATH'
if its argument contains no slashes. Also, some shells, including
bash 3.2, implicitly append the current directory to this `PATH'
search, even though Posix forbids it. So if you want to use `.'
on a file `foo' in the current directory, you must use `. ./foo'.
Not all shells gracefully handle syntax errors within a sourced
file. On one extreme, some non-interactive shells abort the
entire script. On the other, `zsh' 4.3.10 has a bug where it
fails to react to the syntax error.
$ echo 'fi' > syntax
$ bash -c '. ./syntax; echo $?'
./syntax: line 1: syntax error near unexpected token `fi'
./syntax: line 1: `fi'
1
$ ash -c '. ./syntax; echo $?'
./syntax: 1: Syntax error: "fi" unexpected
$ zsh -c '. ./syntax; echo $?'
./syntax:1: parse error near `fi'
0
`!'
The Unix version 7 shell did not support negating the exit status
of commands with `!', and this feature is still absent from some
shells (e.g., Solaris `/bin/sh'). Other shells, such as FreeBSD
`/bin/sh' or `ash', have bugs when using `!':
$ sh -c '! : | :'; echo $?
1
$ ash -c '! : | :'; echo $?
0
$ sh -c '! { :; }'; echo $?
1
$ ash -c '! { :; }'; echo $?
{: not found
Syntax error: "}" unexpected
2
Shell code like this:
if ! cmp file1 file2 >/dev/null 2>&1; then
echo files differ or trouble
fi
is therefore not portable in practice. Typically it is easy to
rewrite such code, e.g.:
cmp file1 file2 >/dev/null 2>&1 ||
echo files differ or trouble
More generally, one can always rewrite `! COMMAND' as:
if COMMAND; then (exit 1); else :; fi
`{...}'
Bash 3.2 (and earlier versions) sometimes does not properly set
`$?' when failing to write redirected output of a compound command.
This problem is most commonly observed with `{...}'; it does not
occur with `(...)'. For example:
$ bash -c '{ echo foo; } >/bad; echo $?'
bash: line 1: /bad: Permission denied
0
$ bash -c 'while :; do echo; done >/bad; echo $?'
bash: line 1: /bad: Permission denied
0
To work around the bug, prepend `:;':
$ bash -c ':;{ echo foo; } >/bad; echo $?'
bash: line 1: /bad: Permission denied
1
Posix requires a syntax error if a brace list has no contents.
However, not all shells obey this rule; and on shells where empty
lists are permitted, the effect on `$?' is inconsistent. To avoid
problems, ensure that a brace list is never empty.
$ bash -c 'false; { }; echo $?' || echo $?
bash: line 1: syntax error near unexpected token `}'
bash: line 1: `false; { }; echo $?'
2
$ zsh -c 'false; { }; echo $?' || echo $?
1
$ pdksh -c 'false; { }; echo $?' || echo $?
0
`break'
The use of `break 2' etc. is safe.
`case'
You don't need to quote the argument; no splitting is performed.
You don't need the final `;;', but you should use it.
Posix requires support for `case' patterns with opening
parentheses like this:
case $file_name in
(*.c) echo "C source code";;
esac
but the `(' in this example is not portable to many Bourne shell
implementations, which is a pity for those of us using tools that
rely on balanced parentheses. For instance, with Solaris
`/bin/sh':
$ case foo in (foo) echo foo;; esac
error-->syntax error: `(' unexpected
The leading `(' can be omitted safely. Unfortunately, there are
contexts where unbalanced parentheses cause other problems, such
as when using a syntax-highlighting editor that searches for the
balancing counterpart, or more importantly, when using a case
statement as an underquoted argument to an Autoconf macro. *Note
Balancing Parentheses::, for tradeoffs involved in various styles
of dealing with unbalanced `)'.
Zsh handles pattern fragments derived from parameter expansions or
command substitutions as though quoted:
$ pat=\?; case aa in ?$pat) echo match;; esac
$ pat=\?; case a? in ?$pat) echo match;; esac
match
Because of a bug in its `fnmatch', Bash fails to properly handle
backslashes in character classes:
bash-2.02$ case /tmp in [/\\]*) echo OK;; esac
bash-2.02$
This is extremely unfortunate, since you are likely to use this
code to handle Posix or MS-DOS absolute file names. To work
around this bug, always put the backslash first:
bash-2.02$ case '\TMP' in [\\/]*) echo OK;; esac
OK
bash-2.02$ case /tmp in [\\/]*) echo OK;; esac
OK
Many Bourne shells cannot handle closing brackets in character
classes correctly.
Some shells also have problems with backslash escaping in case you
do not want to match the backslash: both a backslash and the
escaped character match this pattern. To work around this,
specify the character class in a variable, so that quote removal
does not apply afterwards, and the special characters don't have
to be backslash-escaped:
$ case '\' in [\Syntax error: ";" unexpected (expecting ")")
Posix requires `case' to give an exit status of 0 if no cases
match. However, `/bin/sh' in Solaris 10 does not obey this rule.
Meanwhile, it is unclear whether a case that matches, but contains
no statements, must also change the exit status to 0. The M4sh
macro `AS_CASE' works around these inconsistencies.
$ bash -c 'case `false` in ?) ;; esac; echo $?'
0
$ /bin/sh -c 'case `false` in ?) ;; esac; echo $?'
255
`cd'
Posix 1003.1-2001 requires that `cd' must support the `-L'
("logical") and `-P' ("physical") options, with `-L' being the
default. However, traditional shells do not support these
options, and their `cd' command has the `-P' behavior.
Portable scripts should assume neither option is supported, and
should assume neither behavior is the default. This can be a bit
tricky, since the Posix default behavior means that, for example,
`ls ..' and `cd ..' may refer to different directories if the
current logical directory is a symbolic link. It is safe to use
`cd DIR' if DIR contains no `..' components. Also,
Autoconf-generated scripts check for this problem when computing
variables like `ac_top_srcdir' (*note Configuration Actions::), so
it is safe to `cd' to these variables.
Posix states that behavior is undefined if `cd' is given an
explicit empty argument. Some shells do nothing, some change to
the first entry in `CDPATH', some change to `HOME', and some exit
the shell rather than returning an error. Unfortunately, this
means that if `$var' is empty, then `cd "$var"' is less predictable
than `cd $var' (at least the latter is well-behaved in all shells
at changing to `HOME', although this is probably not what you
wanted in a script). You should check that a directory name was
supplied before trying to change locations.
*Note Special Shell Variables::, for portability problems involving
`cd' and the `CDPATH' environment variable. Also please see the
discussion of the `pwd' command.
`echo'
The simple `echo' is probably the most surprising source of
portability troubles. It is not possible to use `echo' portably
unless both options and escape sequences are omitted. Don't
expect any option.
Do not use backslashes in the arguments, as there is no consensus
on their handling. For `echo '\n' | wc -l', the `sh' of Solaris
outputs 2, but Bash and Zsh (in `sh' emulation mode) output 1.
The problem is truly `echo': all the shells understand `'\n'' as
the string composed of a backslash and an `n'. Within a command
substitution, `echo 'string\c'' will mess up the internal state of
ksh88 on AIX 6.1 so that it will print the first character `s'
only, followed by a newline, and then entirely drop the output of
the next echo in a command substitution.
Because of these problems, do not pass a string containing
arbitrary characters to `echo'. For example, `echo "$foo"' is safe
only if you know that FOO's value cannot contain backslashes and
cannot start with `-'.
If this may not be true, `printf' is in general safer and easier
to use than `echo' and `echo -n'. Thus, scripts where portability
is not a major concern should use `printf '%s\n'' whenever `echo'
could fail, and similarly use `printf %s' instead of `echo -n'.
For portable shell scripts, instead, it is suggested to use a
here-document like this:
cat <bar'',
since it mistakenly replaces the contents of `bar' by the string
`cat foo'. No simple, general, and portable solution to this
problem is known.
`exec'
Posix describes several categories of shell built-ins. Special
built-ins (such as `exit') must impact the environment of the
current shell, and need not be available through `exec'. All
other built-ins are regular, and must not propagate variable
assignments to the environment of the current shell. However, the
group of regular built-ins is further distinguished by commands
that do not require a `PATH' search (such as `cd'), in contrast to
built-ins that are offered as a more efficient version of
something that must still be found in a `PATH' search (such as
`echo'). Posix is not clear on whether `exec' must work with the
list of 17 utilities that are invoked without a `PATH' search, and
many platforms lack an executable for some of those built-ins:
$ sh -c 'exec cd /tmp'
sh: line 0: exec: cd: not found
All other built-ins that provide utilities specified by Posix must
have a counterpart executable that exists on `PATH', although Posix
allows `exec' to use the built-in instead of the executable. For
example, contrast `bash' 3.2 and `pdksh' 5.2.14:
$ bash -c 'pwd --version' | head -n1
bash: line 0: pwd: --: invalid option
pwd: usage: pwd [-LP]
$ bash -c 'exec pwd --version' | head -n1
pwd (GNU coreutils) 6.10
$ pdksh -c 'exec pwd --version' | head -n1
pdksh: pwd: --: unknown option
When it is desired to avoid a regular shell built-in, the
workaround is to use some other forwarding command, such as `env'
or `nice', that will ensure a path search:
$ pdksh -c 'exec true --version' | head -n1
$ pdksh -c 'nice true --version' | head -n1
true (GNU coreutils) 6.10
$ pdksh -c 'env true --version' | head -n1
true (GNU coreutils) 6.10
`exit'
The default value of `exit' is supposed to be `$?'; unfortunately,
some shells, such as the DJGPP port of Bash 2.04, just perform
`exit 0'.
bash-2.04$ foo=`exit 1` || echo fail
fail
bash-2.04$ foo=`(exit 1)` || echo fail
fail
bash-2.04$ foo=`(exit 1); exit` || echo fail
bash-2.04$
Using `exit $?' restores the expected behavior.
Some shell scripts, such as those generated by `autoconf', use a
trap to clean up before exiting. If the last shell command exited
with nonzero status, the trap also exits with nonzero status so
that the invoker can tell that an error occurred.
Unfortunately, in some shells, such as Solaris `/bin/sh', an exit
trap ignores the `exit' command's argument. In these shells, a
trap cannot determine whether it was invoked by plain `exit' or by
`exit 1'. Instead of calling `exit' directly, use the
`AC_MSG_ERROR' macro that has a workaround for this problem.
`export'
The builtin `export' dubs a shell variable "environment variable".
Each update of exported variables corresponds to an update of the
environment variables. Conversely, each environment variable
received by the shell when it is launched should be imported as a
shell variable marked as exported.
Alas, many shells, such as Solaris `/bin/sh', IRIX 6.3, IRIX 5.2,
AIX 4.1.5, and Digital Unix 4.0, forget to `export' the
environment variables they receive. As a result, two variables
coexist: the environment variable and the shell variable. The
following code demonstrates this failure:
#!/bin/sh
echo $FOO
FOO=bar
echo $FOO
exec /bin/sh $0
when run with `FOO=foo' in the environment, these shells print
alternately `foo' and `bar', although they should print only `foo'
and then a sequence of `bar's.
Therefore you should `export' again each environment variable that
you update; the export can occur before or after the assignment.
Posix is not clear on whether the `export' of an undefined
variable causes the variable to be defined with the value of an
empty string, or merely marks any future definition of a variable
by that name for export. Various shells behave differently in
this regard:
$ sh -c 'export foo; env | grep foo'
$ ash -c 'export foo; env | grep foo'
foo=
Posix requires `export' to honor assignments made as arguments,
but older shells do not support this, including `/bin/sh' in
Solaris 10. Portable scripts should separate assignments and
exports into different statements.
$ bash -c 'export foo=bar; echo $foo'
bar
$ /bin/sh -c 'export foo=bar; echo $foo'
/bin/sh: foo=bar: is not an identifier
$ /bin/sh -c 'export foo; foo=bar; echo $foo'
bar
`false'
Don't expect `false' to exit with status 1: in native Solaris
`/bin/false' exits with status 255.
`for'
To loop over positional arguments, use:
for arg
do
echo "$arg"
done
You may _not_ leave the `do' on the same line as `for', since some
shells improperly grok:
for arg; do
echo "$arg"
done
If you want to explicitly refer to the positional arguments, given
the `$@' bug (*note Shell Substitutions::), use:
for arg in ${1+"$@"}; do
echo "$arg"
done
But keep in mind that Zsh, even in Bourne shell emulation mode,
performs word splitting on `${1+"$@"}'; see *note Shell
Substitutions::, item `$@', for more.
In Solaris `/bin/sh', when the list of arguments of a `for' loop
starts with _unquoted_ tokens looking like variable assignments,
the loop is not executed on those tokens:
$ /bin/sh -c 'for v in a=b c=d x e=f; do echo $v; done'
x
e=f
Thankfully, quoting the assignment-like tokens, or starting the
list with other tokens (including unquoted variable expansion that
results in an assignment-like result), avoids the problem, so it
is easy to work around:
$ /bin/sh -c 'for v in "a=b"; do echo $v; done'
a=b
$ /bin/sh -c 'x=a=b; for v in $x c=d; do echo $v; done'
a=b
c=d
`if'
Using `!' is not portable. Instead of:
if ! cmp -s file file.new; then
mv file.new file
fi
use:
if cmp -s file file.new; then :; else
mv file.new file
fi
Or, especially if the "else" branch is short, you can use `||'.
In M4sh, the `AS_IF' macro provides an easy way to write these
kinds of conditionals:
AS_IF([cmp -s file file.new], [], [mv file.new file])
This is especially useful in other M4 macros, where the "then" and
"else" branches might be macro arguments.
Some very old shells did not reset the exit status from an `if'
with no `else':
$ if (exit 42); then true; fi; echo $?
42
whereas a proper shell should have printed `0'. But this is no
longer a portability problem; any shell that supports functions
gets it correct. However, it explains why some makefiles have
lengthy constructs:
if test -f "$file"; then
install "$file" "$dest"
else
:
fi
`printf'
A format string starting with a `-' can cause problems. Bash
interprets it as an option and gives an error. And `--' to mark
the end of options is not good in the NetBSD Almquist shell (e.g.,
0.4.6) which takes that literally as the format string. Putting
the `-' in a `%c' or `%s' is probably easiest:
printf %s -foo
Bash 2.03 mishandles an escape sequence that happens to evaluate
to `%':
$ printf '\045'
bash: printf: `%': missing format character
Large outputs may cause trouble. On Solaris 2.5.1 through 10, for
example, `/usr/bin/printf' is buggy, so when using `/bin/sh' the
command `printf %010000x 123' normally dumps core.
Since `printf' is not always a shell builtin, there is a potential
speed penalty for using `printf '%s\n'' as a replacement for an
`echo' that does not interpret `\' or leading `-'. With Solaris
`ksh', it is possible to use `print -r --' for this role instead.
*Note Limitations of Shell Builtins: echo for a discussion of
portable alternatives to both `printf' and `echo'.
`pwd'
With modern shells, plain `pwd' outputs a "logical" directory
name, some of whose components may be symbolic links. These
directory names are in contrast to "physical" directory names,
whose components are all directories.
Posix 1003.1-2001 requires that `pwd' must support the `-L'
("logical") and `-P' ("physical") options, with `-L' being the
default. However, traditional shells do not support these
options, and their `pwd' command has the `-P' behavior.
Portable scripts should assume neither option is supported, and
should assume neither behavior is the default. Also, on many hosts
`/bin/pwd' is equivalent to `pwd -P', but Posix does not require
this behavior and portable scripts should not rely on it.
Typically it's best to use plain `pwd'. On modern hosts this
outputs logical directory names, which have the following
advantages:
* Logical names are what the user specified.
* Physical names may not be portable from one installation host
to another due to network file system gymnastics.
* On modern hosts `pwd -P' may fail due to lack of permissions
to some parent directory, but plain `pwd' cannot fail for this
reason.
Also please see the discussion of the `cd' command.
`read'
No options are portable, not even support `-r' (Solaris `/bin/sh'
for example). Tru64/OSF 5.1 `sh' treats `read' as a special
built-in, so it may exit if input is redirected from a
non-existent or unreadable file.
`set'
With the FreeBSD 6.0 shell, the `set' command (without any
options) does not sort its output.
The `set' builtin faces the usual problem with arguments starting
with a dash. Modern shells such as Bash or Zsh understand `--' to
specify the end of the options (any argument after `--' is a
parameter, even `-x' for instance), but many traditional shells
(e.g., Solaris 10 `/bin/sh') simply stop option processing as soon
as a non-option argument is found. Therefore, use `dummy' or
simply `x' to end the option processing, and use `shift' to pop it
out:
set x $my_list; shift
Avoid `set -', e.g., `set - $my_list'. Posix no longer requires
support for this command, and in traditional shells `set -
$my_list' resets the `-v' and `-x' options, which makes scripts
harder to debug.
Some nonstandard shells do not recognize more than one option
(e.g., `set -e -x' assigns `-x' to the command line). It is
better to combine them:
set -ex
The option `-e' has historically been underspecified, with enough
ambiguities to cause numerous differences across various shell
implementations; see for example this overview
(http://www.in-ulm.de/~mascheck/various/set-e/), or this link
(http://www.austingroupbugs.net/view.php?id=52), documenting a
change to Posix 2008 to match `ksh88' behavior. Note that mixing
`set -e' and shell functions is asking for surprises:
set -e
doit()
{
rm file
echo one
}
doit || echo two
According to the recommendation, `one' should always be output
regardless of whether the `rm' failed, because it occurs within
the body of the shell function `doit' invoked on the left side of
`||', where the effects of `set -e' are not enforced. Likewise,
`two' should never be printed, since the failure of `rm' does not
abort the function, such that the status of `doit' is 0.
The BSD shell has had several problems with the `-e' option.
Older versions of the BSD shell (circa 1990) mishandled `&&',
`||', `if', and `case' when `-e' was in effect, causing the shell
to exit unexpectedly in some cases. This was particularly a
problem with makefiles, and led to circumlocutions like `sh -c
'test -f file || touch file'', where the seemingly-unnecessary `sh
-c '...'' wrapper works around the bug (*note Failure in Make
Rules::).
Even relatively-recent versions of the BSD shell (e.g., OpenBSD
3.4) wrongly exit with `-e' if the last command within a compound
statement fails and is guarded by an `&&' only. For example:
#! /bin/sh
set -e
foo=''
test -n "$foo" && exit 1
echo one
if :; then
test -n "$foo" && exit 1
echo two
test -n "$foo" && exit 1
fi
echo three
does not print `three'. One workaround is to change the last
instance of `test -n "$foo" && exit 1' to be `if test -n "$foo";
then exit 1; fi' instead. Another possibility is to warn BSD
users not to use `sh -e'.
When `set -e' is in effect, a failed command substitution in
Solaris `/bin/sh' cannot be ignored, even with `||'.
$ /bin/sh -c 'set -e; foo=`false` || echo foo; echo bar'
$ bash -c 'set -e; foo=`false` || echo foo; echo bar'
foo
bar
Moreover, a command substitution, successful or not, causes this
shell to exit from a failing outer command even in presence of an
`&&' list:
$ bash -c 'set -e; false `true` && echo notreached; echo ok'
ok
$ sh -c 'set -e; false `true` && echo notreached; echo ok'
$
Portable scripts should not use `set -e' if `trap' is used to
install an exit handler. This is because Tru64/OSF 5.1 `sh'
sometimes enters the trap handler with the exit status of the
command prior to the one that triggered the errexit handler:
$ sh -ec 'trap '\''echo $?'\'' 0; false'
0
$ sh -c 'set -e; trap '\''echo $?'\'' 0; false'
1
Thus, when writing a script in M4sh, rather than trying to rely on
`set -e', it is better to append `|| AS_EXIT' to any statement
where it is desirable to abort on failure.
Job control is not provided by all shells, so the use of `set -m'
or `set -b' must be done with care. When using `zsh' in native
mode, asynchronous notification (`set -b') is enabled by default,
and using `emulate sh' to switch to Posix mode does not clear this
setting (although asynchronous notification has no impact unless
job monitoring is also enabled). Also, `zsh' 4.3.10 and earlier
have a bug where job control can be manipulated in interactive
shells, but not in subshells or scripts. Furthermore, some
shells, like `pdksh', fail to treat subshells as interactive, even
though the parent shell was.
$ echo $ZSH_VERSION
4.3.10
$ set -m; echo $?
0
$ zsh -c 'set -m; echo $?'
set: can't change option: -m
$ (set -m); echo $?
set: can't change option: -m
1
$ pdksh -ci 'echo $-; (echo $-)'
cim
c
Use of `set -n' (typically via `sh -n script') to validate a
script is not foolproof. Modern `ksh93' tries to be helpful by
informing you about better syntax, but switching the script to use
the suggested syntax in order to silence the warnings would render
the script no longer portable to older shells:
$ ksh -nc '``'
ksh: warning: line 1: `...` obsolete, use $(...)
0
Furthermore, on ancient hosts, such as SunOS 4, `sh -n' could go
into an infinite loop; even with that bug fixed, Solaris 8
`/bin/sh' takes extremely long to parse large scripts. Autoconf
itself uses `sh -n' within its testsuite to check that correct
scripts were generated, but only after first probing for other
shell features (such as `test -n "${BASH_VERSION+set}"') that
indicate a reasonably fast and working implementation.
`shift'
Not only is `shift'ing a bad idea when there is nothing left to
shift, but in addition it is not portable: the shell of MIPS
RISC/OS 4.52 refuses to do it.
Don't use `shift 2' etc.; while it in the SVR1 shell (1983), it is
also absent in many pre-Posix shells.
`source'
This command is not portable, as Posix does not require it; use
`.' instead.
`test'
The `test' program is the way to perform many file and string
tests. It is often invoked by the alternate name `[', but using
that name in Autoconf code is asking for trouble since it is an M4
quote character.
The `-a', `-o', `(', and `)' operands are not present in all
implementations, and have been marked obsolete by Posix 2008.
This is because there are inherent ambiguities in using them. For
example, `test "$1" -a "$2"' looks like a binary operator to check
whether two strings are both non-empty, but if `$1' is the literal
`!', then some implementations of `test' treat it as a negation of
the unary operator `-a'.
Thus, portable uses of `test' should never have more than four
arguments, and scripts should use shell constructs like `&&' and
`||' instead. If you combine `&&' and `||' in the same statement,
keep in mind that they have equal precedence, so it is often
better to parenthesize even when this is redundant. For example:
# Not portable:
test "X$a" = "X$b" -a \
'(' "X$c" != "X$d" -o "X$e" = "X$f" ')'
# Portable:
test "X$a" = "X$b" &&
{ test "X$c" != "X$d" || test "X$e" = "X$f"; }
`test' does not process options like most other commands do; for
example, it does not recognize the `--' argument as marking the
end of options.
It is safe to use `!' as a `test' operator. For example, `if test
! -d foo; ...' is portable even though `if ! test -d foo; ...' is
not.
`test' (files)
To enable `configure' scripts to support cross-compilation, they
shouldn't do anything that tests features of the build system
instead of the host system. But occasionally you may find it
necessary to check whether some arbitrary file exists. To do so,
use `test -f', `test -r', or `test -x'. Do not use `test -e',
because Solaris 10 `/bin/sh' lacks it. To test for symbolic links
on systems that have them, use `test -h' rather than `test -L';
either form conforms to Posix 1003.1-2001, but older shells like
Solaris 8 `/bin/sh' support only `-h'.
For historical reasons, Posix reluctantly allows implementations of
`test -x' that will succeed for the root user, even if no execute
permissions are present. Furthermore, shells do not all agree on
whether Access Control Lists should affect `test -r', `test -w',
and `test -x'; some shells base test results strictly on the
current user id compared to file owner and mode, as if by
`stat(2)'; while other shells base test results on whether the
current user has the given right, even if that right is only
granted by an ACL, as if by `faccessat(2)'. Furthermore, there is
a classic time of check to time of use race between any use of
`test' followed by operating on the just-checked file. Therefore,
it is a good idea to write scripts that actually attempt an
operation, and are prepared for the resulting failure if
permission is denied, rather than trying to avoid an operation
based solely on whether `test' guessed that it might not be
permitted.
`test' (strings)
Posix says that `test "STRING"' succeeds if STRING is not null,
but this usage is not portable to traditional platforms like
Solaris 10 `/bin/sh', which mishandle strings like `!' and `-n'.
Posix also says that `test ! "STRING"', `test -n "STRING"' and
`test -z "STRING"' work with any string, but many shells (such as
Solaris, AIX 3.2, UNICOS 10.0.0.6, Digital Unix 4, etc.) get
confused if STRING looks like an operator:
$ test -n =
test: argument expected
$ test ! -n
test: argument expected
$ test -z ")"; echo $?
0
Similarly, Posix says that both `test "STRING1" = "STRING2"' and
`test "STRING1" != "STRING2"' work for any pairs of strings, but
in practice this is not true for troublesome strings that look
like operators or parentheses, or that begin with `-'.
It is best to protect such strings with a leading `X', e.g., `test
"XSTRING" != X' rather than `test -n "STRING"' or `test !
"STRING"'.
It is common to find variations of the following idiom:
test -n "`echo $ac_feature | sed 's/[-a-zA-Z0-9_]//g'`" &&
ACTION
to take an action when a token matches a given pattern. Such
constructs should be avoided by using:
case $ac_feature in
*[!-a-zA-Z0-9_]*) ACTION;;
esac
If the pattern is a complicated regular expression that cannot be
expressed as a shell pattern, use something like this instead:
expr "X$ac_feature" : 'X.*[^-a-zA-Z0-9_]' >/dev/null &&
ACTION
`expr "XFOO" : "XBAR"' is more robust than `echo "XFOO" | grep
"^XBAR"', because it avoids problems when `FOO' contains
backslashes.
`trap'
It is safe to trap at least the signals 1, 2, 13, and 15. You can
also trap 0, i.e., have the `trap' run when the script ends
(either via an explicit `exit', or the end of the script). The
trap for 0 should be installed outside of a shell function, or AIX
5.3 `/bin/sh' will invoke the trap at the end of this function.
Posix says that `trap - 1 2 13 15' resets the traps for the
specified signals to their default values, but many common shells
(e.g., Solaris `/bin/sh') misinterpret this and attempt to execute
a "command" named `-' when the specified conditions arise. Posix
2008 also added a requirement to support `trap 1 2 13 15' to reset
traps, as this is supported by a larger set of shells, but there
are still shells like `dash' that mistakenly try to execute `1'
instead of resetting the traps. Therefore, there is no portable
workaround, except for `trap - 0', for which `trap '' 0' is a
portable substitute.
Although Posix is not absolutely clear on this point, it is widely
admitted that when entering the trap `$?' should be set to the exit
status of the last command run before the trap. The ambiguity can
be summarized as: "when the trap is launched by an `exit', what is
the _last_ command run: that before `exit', or `exit' itself?"
Bash considers `exit' to be the last command, while Zsh and
Solaris `/bin/sh' consider that when the trap is run it is _still_
in the `exit', hence it is the previous exit status that the trap
receives:
$ cat trap.sh
trap 'echo $?' 0
(exit 42); exit 0
$ zsh trap.sh
42
$ bash trap.sh
0
The portable solution is then simple: when you want to `exit 42',
run `(exit 42); exit 42', the first `exit' being used to set the
exit status to 42 for Zsh, and the second to trigger the trap and
pass 42 as exit status for Bash. In M4sh, this is covered by using
`AS_EXIT'.
The shell in FreeBSD 4.0 has the following bug: `$?' is reset to 0
by empty lines if the code is inside `trap'.
$ trap 'false
echo $?' 0
$ exit
0
Fortunately, this bug only affects `trap'.
Several shells fail to execute an exit trap that is defined inside
a subshell, when the last command of that subshell is not a
builtin. A workaround is to use `exit $?' as the shell builtin.
$ bash -c '(trap "echo hi" 0; /bin/true)'
hi
$ /bin/sh -c '(trap "echo hi" 0; /bin/true)'
$ /bin/sh -c '(trap "echo hi" 0; /bin/true; exit $?)'
hi
Likewise, older implementations of `bash' failed to preserve `$?'
across an exit trap consisting of a single cleanup command.
$ bash -c 'trap "/bin/true" 0; exit 2'; echo $?
2
$ bash-2.05b -c 'trap "/bin/true" 0; exit 2'; echo $?
0
$ bash-2.05b -c 'trap ":; /bin/true" 0; exit 2'; echo $?
2
`true'
Don't worry: as far as we know `true' is portable. Nevertheless,
it's not always a builtin (e.g., Bash 1.x), and the portable shell
community tends to prefer using `:'. This has a funny side
effect: when asked whether `false' is more portable than `true'
Alexandre Oliva answered:
In a sense, yes, because if it doesn't exist, the shell will
produce an exit status of failure, which is correct for
`false', but not for `true'.
Remember that even though `:' ignores its arguments, it still takes
time to compute those arguments. It is a good idea to use double
quotes around any arguments to `:' to avoid time spent in field
splitting and file name expansion.
`unset'
In some nonconforming shells (e.g., Solaris 10 `/bin/ksh' and
`/usr/xpg4/bin/sh', NetBSD 5.99.43 sh, or Bash 2.05a), `unset FOO'
fails when `FOO' is not set. This can interfere with `set -e'
operation. You can use
FOO=; unset FOO
if you are not sure that `FOO' is set.
A few ancient shells lack `unset' entirely. For some variables
such as `PS1', you can use a neutralizing value instead:
PS1='$ '
Usually, shells that do not support `unset' need less effort to
make the environment sane, so for example is not a problem if you
cannot unset `CDPATH' on those shells. However, Bash 2.01
mishandles `unset MAIL' and `unset MAILPATH' in some cases and
dumps core. So, you should do something like
( (unset MAIL) || exit 1) >/dev/null 2>&1 && unset MAIL || :
*Note Special Shell Variables::, for some neutralizing values.
Also, see *note Limitations of Builtins: export, for the case of
environment variables.
`wait'
The exit status of `wait' is not always reliable.
File: autoconf.info, Node: Limitations of Usual Tools, Prev: Limitations of Builtins, Up: Portable Shell
11.15 Limitations of Usual Tools
================================
The small set of tools you can expect to find on any machine can still
include some limitations you should be aware of.
`awk'
Don't leave white space before the opening parenthesis in a user
function call. Posix does not allow this and GNU Awk rejects it:
$ gawk 'function die () { print "Aaaaarg!" }
BEGIN { die () }'
gawk: cmd. line:2: BEGIN { die () }
gawk: cmd. line:2: ^ parse error
$ gawk 'function die () { print "Aaaaarg!" }
BEGIN { die() }'
Aaaaarg!
Posix says that if a program contains only `BEGIN' actions, and
contains no instances of `getline', then the program merely
executes the actions without reading input. However, traditional
Awk implementations (such as Solaris 10 `awk') read and discard
input in this case. Portable scripts can redirect input from
`/dev/null' to work around the problem. For example:
awk 'BEGIN {print "hello world"}' printf "foo\n|foo\n" | $EGREP '^(|foo|bar)$'
|foo
> printf "bar\nbar|\n" | $EGREP '^(foo|bar|)$'
bar|
> printf "foo\nfoo|\n|bar\nbar\n" | $EGREP '^(foo||bar)$'
foo
|bar
`$EGREP' also suffers the limitations of `grep' (*note Limitations
of Usual Tools: grep.).
`expr'
Not all implementations obey the Posix rule that `--' separates
options from arguments; likewise, not all implementations provide
the extension to Posix that the first argument can be treated as
part of a valid expression rather than an invalid option if it
begins with `-'. When performing arithmetic, use `expr 0 + $var'
if `$var' might be a negative number, to keep `expr' from
interpreting it as an option.
No `expr' keyword starts with `X', so use `expr X"WORD" :
'XREGEX'' to keep `expr' from misinterpreting WORD.
Don't use `length', `substr', `match' and `index'.
`expr' (`|')
You can use `|'. Although Posix does require that `expr '''
return the empty string, it does not specify the result when you
`|' together the empty string (or zero) with the empty string. For
example:
expr '' \| ''
Posix 1003.2-1992 returns the empty string for this case, but
traditional Unix returns `0' (Solaris is one such example). In
Posix 1003.1-2001, the specification was changed to match
traditional Unix's behavior (which is bizarre, but it's too late
to fix this). Please note that the same problem does arise when
the empty string results from a computation, as in:
expr bar : foo \| foo : bar
Avoid this portability problem by avoiding the empty string.
`expr' (`:')
Portable `expr' regular expressions should use `\' to escape only
characters in the string `$()*.0123456789[\^n{}'. For example,
alternation, `\|', is common but Posix does not require its
support, so it should be avoided in portable scripts. Similarly,
`\+' and `\?' should be avoided.
Portable `expr' regular expressions should not begin with `^'.
Patterns are automatically anchored so leading `^' is not needed
anyway.
On the other hand, the behavior of the `$' anchor is not portable
on multi-line strings. Posix is ambiguous whether the anchor
applies to each line, as was done in older versions of the GNU
Core Utilities, or whether it applies only to the end of the
overall string, as in Coreutils 6.0 and most other implementations.
$ baz='foo
> bar'
$ expr "X$baz" : 'X\(foo\)$'
$ expr-5.97 "X$baz" : 'X\(foo\)$'
foo
The Posix standard is ambiguous as to whether `expr 'a' : '\(b\)''
outputs `0' or the empty string. In practice, it outputs the
empty string on most platforms, but portable scripts should not
assume this. For instance, the QNX 4.25 native `expr' returns `0'.
One might think that a way to get a uniform behavior would be to
use the empty string as a default value:
expr a : '\(b\)' \| ''
Unfortunately this behaves exactly as the original expression; see
the `expr' (`|') entry for more information.
Some ancient `expr' implementations (e.g., SunOS 4 `expr' and
Solaris 8 `/usr/ucb/expr') have a silly length limit that causes
`expr' to fail if the matched substring is longer than 120 bytes.
In this case, you might want to fall back on `echo|sed' if `expr'
fails. Nowadays this is of practical importance only for the rare
installer who mistakenly puts `/usr/ucb' before `/usr/bin' in
`PATH'.
On Mac OS X 10.4, `expr' mishandles the pattern `[^-]' in some
cases. For example, the command
expr Xpowerpc-apple-darwin8.1.0 : 'X[^-]*-[^-]*-\(.*\)'
outputs `apple-darwin8.1.0' rather than the correct `darwin8.1.0'.
This particular case can be worked around by substituting `[^--]'
for `[^-]'.
Don't leave, there is some more!
The QNX 4.25 `expr', in addition of preferring `0' to the empty
string, has a funny behavior in its exit status: it's always 1
when parentheses are used!
$ val=`expr 'a' : 'a'`; echo "$?: $val"
0: 1
$ val=`expr 'a' : 'b'`; echo "$?: $val"
1: 0
$ val=`expr 'a' : '\(a\)'`; echo "?: $val"
1: a
$ val=`expr 'a' : '\(b\)'`; echo "?: $val"
1: 0
In practice this can be a big problem if you are ready to catch
failures of `expr' programs with some other method (such as using
`sed'), since you may get twice the result. For instance
$ expr 'a' : '\(a\)' || echo 'a' | sed 's/^\(a\)$/\1/'
outputs `a' on most hosts, but `aa' on QNX 4.25. A simple
workaround consists of testing `expr' and using a variable set to
`expr' or to `false' according to the result.
Tru64 `expr' incorrectly treats the result as a number, if it can
be interpreted that way:
$ expr 00001 : '.*\(...\)'
1
On HP-UX 11, `expr' only supports a single sub-expression.
$ expr 'Xfoo' : 'X\(f\(oo\)*\)$'
expr: More than one '\(' was used.
`fgrep'
Posix 1003.1-2001 no longer requires `fgrep', but many hosts do
not yet support the Posix replacement `grep -F'. Also, some
traditional implementations do not work on long input lines. To
work around these problems, invoke `AC_PROG_FGREP' and then use
`$FGREP'.
Tru64/OSF 5.1 `fgrep' does not match an empty pattern.
`find'
The option `-maxdepth' seems to be GNU specific. Tru64 v5.1,
NetBSD 1.5 and Solaris `find' commands do not understand it.
The replacement of `{}' is guaranteed only if the argument is
exactly _{}_, not if it's only a part of an argument. For
instance on DU, and HP-UX 10.20 and HP-UX 11:
$ touch foo
$ find . -name foo -exec echo "{}-{}" \;
{}-{}
while GNU `find' reports `./foo-./foo'.
`grep'
Portable scripts can rely on the `grep' options `-c', `-l', `-n',
and `-v', but should avoid other options. For example, don't use
`-w', as Posix does not require it and Irix 6.5.16m's `grep' does
not support it. Also, portable scripts should not combine `-c'
with `-l', as Posix does not allow this.
Some of the options required by Posix are not portable in practice.
Don't use `grep -q' to suppress output, because many `grep'
implementations (e.g., Solaris) do not support `-q'. Don't use
`grep -s' to suppress output either, because Posix says `-s' does
not suppress output, only some error messages; also, the `-s'
option of traditional `grep' behaved like `-q' does in most modern
implementations. Instead, redirect the standard output and
standard error (in case the file doesn't exist) of `grep' to
`/dev/null'. Check the exit status of `grep' to determine whether
it found a match.
The QNX4 implementation fails to count lines with `grep -c '$'',
but works with `grep -c '^''. Other alternatives for counting
lines are to use `sed -n '$='' or `wc -l'.
Some traditional `grep' implementations do not work on long input
lines. On AIX the default `grep' silently truncates long lines on
the input before matching.
Also, many implementations do not support multiple regexps with
`-e': they either reject `-e' entirely (e.g., Solaris) or honor
only the last pattern (e.g., IRIX 6.5 and NeXT). To work around
these problems, invoke `AC_PROG_GREP' and then use `$GREP'.
Another possible workaround for the multiple `-e' problem is to
separate the patterns by newlines, for example:
grep 'foo
bar' in.txt
except that this fails with traditional `grep' implementations and
with OpenBSD 3.8 `grep'.
Traditional `grep' implementations (e.g., Solaris) do not support
the `-E' or `-F' options. To work around these problems, invoke
`AC_PROG_EGREP' and then use `$EGREP', and similarly for
`AC_PROG_FGREP' and `$FGREP'. Even if you are willing to require
support for Posix `grep', your script should not use both `-E' and
`-F', since Posix does not allow this combination.
Portable `grep' regular expressions should use `\' only to escape
characters in the string `$()*.0123456789[\^{}'. For example,
alternation, `\|', is common but Posix does not require its
support in basic regular expressions, so it should be avoided in
portable scripts. Solaris and HP-UX `grep' do not support it.
Similarly, the following escape sequences should also be avoided:
`\', `\+', `\?', `\`', `\'', `\B', `\b', `\S', `\s', `\W',
and `\w'.
Posix does not specify the behavior of `grep' on binary files. An
example where this matters is using BSD `grep' to search text that
includes embedded ANSI escape sequences for colored output to
terminals (`\033[m' is the sequence to restore normal output); the
behavior depends on whether input is seekable:
$ printf 'esc\033[mape\n' > sample
$ grep . sample
Binary file sample matches
$ cat sample | grep .
escape
`join'
Solaris 8 `join' has bugs when the second operand is standard
input, and when standard input is a pipe. For example, the
following shell script causes Solaris 8 `join' to loop forever:
cat >file </dev/null`' did not always work, since it
was equivalent to `sources='*.c not found'' in the absence of `.c'
files. This is no longer a practical problem, since current `ls'
implementations send diagnostics to standard error.
The behavior of `ls' on a directory that is being concurrently
modified is not always predictable, because of a data race where
cached information returned by `readdir' does not match the current
directory state. In fact, MacOS 10.5 has an intermittent bug where
`readdir', and thus `ls', sometimes lists a file more than once if
other files were added or removed from the directory immediately
prior to the `ls' call. Since `ls' already sorts its output, the
duplicate entries can be avoided by piping the results through
`uniq'.
`mkdir'
No `mkdir' option is portable to older systems. Instead of `mkdir
-p FILE-NAME', you should use `AS_MKDIR_P(FILE-NAME)' (*note
Programming in M4sh::) or `AC_PROG_MKDIR_P' (*note Particular
Programs::).
Combining the `-m' and `-p' options, as in `mkdir -m go-w -p DIR',
often leads to trouble. FreeBSD `mkdir' incorrectly attempts to
change the permissions of DIR even if it already exists. HP-UX
11.23 and IRIX 6.5 `mkdir' often assign the wrong permissions to
any newly-created parents of DIR.
Posix does not clearly specify whether `mkdir -p foo' should
succeed when `foo' is a symbolic link to an already-existing
directory. The GNU Core Utilities 5.1.0 `mkdir' succeeds, but
Solaris `mkdir' fails.
Traditional `mkdir -p' implementations suffer from race conditions.
For example, if you invoke `mkdir -p a/b' and `mkdir -p a/c' at
the same time, both processes might detect that `a' is missing,
one might create `a', then the other might try to create `a' and
fail with a `File exists' diagnostic. The GNU Core Utilities
(`fileutils' version 4.1), FreeBSD 5.0, NetBSD 2.0.2, and OpenBSD
2.4 are known to be race-free when two processes invoke `mkdir -p'
simultaneously, but earlier versions are vulnerable. Solaris
`mkdir' is still vulnerable as of Solaris 10, and other
traditional Unix systems are probably vulnerable too. This
possible race is harmful in parallel builds when several Make
rules call `mkdir -p' to construct directories. You may use
`install-sh -d' as a safe replacement, provided this script is
recent enough; the copy shipped with Autoconf 2.60 and Automake
1.10 is OK, but copies from older versions are vulnerable.
`mkfifo'
`mknod'
The GNU Coding Standards state that `mknod' is safe to use on
platforms where it has been tested to exist; but it is generally
portable only for creating named FIFOs, since device numbers are
platform-specific. Autotest uses `mkfifo' to implement parallel
testsuites. Posix states that behavior is unspecified when
opening a named FIFO for both reading and writing; on at least
Cygwin, this results in failure on any attempt to read or write to
that file descriptor.
`mktemp'
Shell scripts can use temporary files safely with `mktemp', but it
does not exist on all systems. A portable way to create a safe
temporary file name is to create a temporary directory with mode
700 and use a file inside this directory. Both methods prevent
attackers from gaining control, though `mktemp' is far less likely
to fail gratuitously under attack.
Here is sample code to create a new temporary directory `$dir'
safely:
# Create a temporary directory $dir in $TMPDIR (default /tmp).
# Use mktemp if possible; otherwise fall back on mkdir,
# with $RANDOM to make collisions less likely.
: "${TMPDIR:=/tmp}"
{
dir=`
(umask 077 && mktemp -d "$TMPDIR/fooXXXXXX") 2>/dev/null
` &&
test -d "$dir"
} || {
dir=$TMPDIR/foo$$-$RANDOM
(umask 077 && mkdir "$dir")
} || exit $?
`mv'
The only portable options are `-f' and `-i'.
Moving individual files between file systems is portable (it was
in Unix version 6), but it is not always atomic: when doing `mv
new existing', there's a critical section where neither the old
nor the new version of `existing' actually exists.
On some systems moving files from `/tmp' can sometimes cause
undesirable (but perfectly valid) warnings, even if you created
these files. This is because `/tmp' belongs to a group that
ordinary users are not members of, and files created in `/tmp'
inherit the group of `/tmp'. When the file is copied, `mv' issues
a diagnostic without failing:
$ touch /tmp/foo
$ mv /tmp/foo .
error-->mv: ./foo: set owner/group (was: 100/0): Operation not permitted
$ echo $?
0
$ ls foo
foo
This annoying behavior conforms to Posix, unfortunately.
Moving directories across mount points is not portable, use `cp'
and `rm'.
DOS variants cannot rename or remove open files, and do not
support commands like `mv foo bar >foo', even though this is
perfectly portable among Posix hosts.
`od'
In Mac OS X 10.3, `od' does not support the standard Posix options
`-A', `-j', `-N', or `-t', or the XSI option `-s'. The only
supported Posix option is `-v', and the only supported XSI options
are those in `-bcdox'. The BSD `hexdump' program can be used
instead.
This problem no longer exists in Mac OS X 10.4.3.
`rm'
The `-f' and `-r' options are portable.
It is not portable to invoke `rm' without options or operands. On
the other hand, Posix now requires `rm -f' to silently succeed
when there are no operands (useful for constructs like `rm -rf
$filelist' without first checking if `$filelist' was empty). But
this was not always portable; at least NetBSD `rm' built before
2008 would fail with a diagnostic.
A file might not be removed even if its parent directory is
writable and searchable. Many Posix hosts cannot remove a mount
point, a named stream, a working directory, or a last link to a
file that is being executed.
DOS variants cannot rename or remove open files, and do not
support commands like `rm foo >foo', even though this is perfectly
portable among Posix hosts.
`rmdir'
Just as with `rm', some platforms refuse to remove a working
directory.
`sed'
Patterns should not include the separator (unless escaped), even
as part of a character class. In conformance with Posix, the Cray
`sed' rejects `s/[^/]*$//': use `s%[^/]*$%%'. Even when escaped,
patterns should not include separators that are also used as `sed'
metacharacters. For example, GNU sed 4.0.9 rejects
`s,x\{1\,\},,', while sed 4.1 strips the backslash before the comma
before evaluating the basic regular expression.
Avoid empty patterns within parentheses (i.e., `\(\)'). Posix does
not require support for empty patterns, and Unicos 9 `sed' rejects
them.
Unicos 9 `sed' loops endlessly on patterns like `.*\n.*'.
Sed scripts should not use branch labels longer than 7 characters
and should not contain comments; AIX 5.3 `sed' rejects indented
comments. HP-UX sed has a limit of 99 commands (not counting `:'
commands) and 48 labels, which cannot be circumvented by using
more than one script file. It can execute up to 19 reads with the
`r' command per cycle. Solaris `/usr/ucb/sed' rejects usages that
exceed a limit of about 6000 bytes for the internal representation
of commands.
Avoid redundant `;', as some `sed' implementations, such as NetBSD
1.4.2's, incorrectly try to interpret the second `;' as a command:
$ echo a | sed 's/x/x/;;s/x/x/'
sed: 1: "s/x/x/;;s/x/x/": invalid command code ;
Some `sed' implementations have a buffer limited to 4000 bytes,
and this limits the size of input lines, output lines, and internal
buffers that can be processed portably. Likewise, not all `sed'
implementations can handle embedded `NUL' or a missing trailing
newline.
Remember that ranges within a bracket expression of a regular
expression are only well-defined in the `C' (or `POSIX') locale.
Meanwhile, support for character classes like `[[:upper:]]' is not
yet universal, so if you cannot guarantee the setting of `LC_ALL',
it is better to spell out a range `[ABCDEFGHIJKLMNOPQRSTUVWXYZ]'
than to rely on `[A-Z]'.
Additionally, Posix states that regular expressions are only
well-defined on characters. Unfortunately, there exist platforms
such as MacOS X 10.5 where not all 8-bit byte values are valid
characters, even though that platform has a single-byte `C'
locale. And Posix allows the existence of a multi-byte `C'
locale, although that does not yet appear to be a common
implementation. At any rate, it means that not all bytes will be
matched by the regular expression `.':
$ printf '\200\n' | LC_ALL=C sed -n /./p | wc -l
0
$ printf '\200\n' | LC_ALL=en_US.ISO8859-1 sed -n /./p | wc -l
1
Portable `sed' regular expressions should use `\' only to escape
characters in the string `$()*.0123456789[\^n{}'. For example,
alternation, `\|', is common but Posix does not require its
support, so it should be avoided in portable scripts. Solaris
`sed' does not support alternation; e.g., `sed '/a\|b/d'' deletes
only lines that contain the literal string `a|b'. Similarly, `\+'
and `\?' should be avoided.
Anchors (`^' and `$') inside groups are not portable.
Nested parentheses in patterns (e.g., `\(\(a*\)b*)\)') are quite
portable to current hosts, but was not supported by some ancient
`sed' implementations like SVR3.
Some `sed' implementations, e.g., Solaris, restrict the special
role of the asterisk `*' to one-character regular expressions and
back-references, and the special role of interval expressions
`\{M\}', `\{M,\}', or `\{M,N\}' to one-character regular
expressions. This may lead to unexpected behavior:
$ echo '1*23*4' | /usr/bin/sed 's/\(.\)*/x/g'
x2x4
$ echo '1*23*4' | /usr/xpg4/bin/sed 's/\(.\)*/x/g'
x
The `-e' option is mostly portable. However, its argument cannot
start with `a', `c', or `i', as this runs afoul of a Tru64 5.1 bug.
Also, its argument cannot be empty, as this fails on AIX 5.3.
Some people prefer to use `-e':
sed -e 'COMMAND-1' \
-e 'COMMAND-2'
as opposed to the equivalent:
sed '
COMMAND-1
COMMAND-2
'
The following usage is sometimes equivalent:
sed 'COMMAND-1;COMMAND-2'
but Posix says that this use of a semicolon has undefined effect if
COMMAND-1's verb is `{', `a', `b', `c', `i', `r', `t', `w', `:',
or `#', so you should use semicolon only with simple scripts that
do not use these verbs.
Posix up to the 2008 revision requires the argument of the `-e'
option to be a syntactically complete script. GNU `sed' allows to
pass multiple script fragments, each as argument of a separate
`-e' option, that are then combined, with newlines between the
fragments, and a future Posix revision may allow this as well.
This approach is not portable with script fragments ending in
backslash; for example, the `sed' programs on Solaris 10, HP-UX
11, and AIX don't allow splitting in this case:
$ echo a | sed -n -e 'i\
0'
0
$ echo a | sed -n -e 'i\' -e 0
Unrecognized command: 0
In practice, however, this technique of joining fragments through
`-e' works for multiple `sed' functions within `{' and `}', even
if that is not specified by Posix:
$ echo a | sed -n -e '/a/{' -e s/a/b/ -e p -e '}'
b
Commands inside { } brackets are further restricted. Posix 2008
says that they cannot be preceded by addresses, `!', or `;', and
that each command must be followed immediately by a newline,
without any intervening blanks or semicolons. The closing bracket
must be alone on a line, other than white space preceding or
following it. However, a future version of Posix may standardize
the use of addresses within brackets.
Contrary to yet another urban legend, you may portably use `&' in
the replacement part of the `s' command to mean "what was
matched". All descendants of Unix version 7 `sed' (at least; we
don't have first hand experience with older `sed' implementations)
have supported it.
Posix requires that you must not have any white space between `!'
and the following command. It is OK to have blanks between the
address and the `!'. For instance, on Solaris:
$ echo "foo" | sed -n '/bar/ ! p'
error-->Unrecognized command: /bar/ ! p
$ echo "foo" | sed -n '/bar/! p'
error-->Unrecognized command: /bar/! p
$ echo "foo" | sed -n '/bar/ !p'
foo
Posix also says that you should not combine `!' and `;'. If you
use `!', it is best to put it on a command that is delimited by
newlines rather than `;'.
Also note that Posix requires that the `b', `t', `r', and `w'
commands be followed by exactly one space before their argument.
On the other hand, no white space is allowed between `:' and the
subsequent label name.
If a sed script is specified on the command line and ends in an
`a', `c', or `i' command, the last line of inserted text should be
followed by a newline. Otherwise some `sed' implementations
(e.g., OpenBSD 3.9) do not append a newline to the inserted text.
Many `sed' implementations (e.g., MacOS X 10.4, OpenBSD 3.9,
Solaris 10 `/usr/ucb/sed') strip leading white space from the text
of `a', `c', and `i' commands. Prepend a backslash to work around
this incompatibility with Posix:
$ echo flushleft | sed 'a\
> indented
> '
flushleft
indented
$ echo foo | sed 'a\
> \ indented
> '
flushleft
indented
Posix requires that with an empty regular expression, the last
non-empty regular expression from either an address specification
or substitution command is applied. However, busybox 1.6.1
complains when using a substitution command with a replacement
containing a back-reference to an empty regular expression; the
workaround is repeating the regular expression.
$ echo abc | busybox sed '/a\(b\)c/ s//\1/'
sed: No previous regexp.
$ echo abc | busybox sed '/a\(b\)c/ s/a\(b\)c/\1/'
b
`sed' (`t')
Some old systems have `sed' that "forget" to reset their `t' flag
when starting a new cycle. For instance on MIPS RISC/OS, and on
IRIX 5.3, if you run the following `sed' script (the line numbers
are not actual part of the texts):
s/keep me/kept/g # a
t end # b
s/.*/deleted/g # c
:end # d
on
delete me # 1
delete me # 2
keep me # 3
delete me # 4
you get
deleted
delete me
kept
deleted
instead of
deleted
deleted
kept
deleted
Why? When processing line 1, (c) matches, therefore sets the `t'
flag, and the output is produced. When processing line 2, the `t'
flag is still set (this is the bug). Command (a) fails to match,
but `sed' is not supposed to clear the `t' flag when a
substitution fails. Command (b) sees that the flag is set,
therefore it clears it, and jumps to (d), hence you get `delete me'
instead of `deleted'. When processing line (3), `t' is clear, (a)
matches, so the flag is set, hence (b) clears the flags and jumps.
Finally, since the flag is clear, line 4 is processed properly.
There are two things one should remember about `t' in `sed'.
Firstly, always remember that `t' jumps if _some_ substitution
succeeded, not only the immediately preceding substitution.
Therefore, always use a fake `t clear' followed by a `:clear' on
the next line, to reset the `t' flag where needed.
Secondly, you cannot rely on `sed' to clear the flag at each new
cycle.
One portable implementation of the script above is:
t clear
:clear
s/keep me/kept/g
t end
s/.*/deleted/g
:end
`sleep'
Using `sleep' is generally portable. However, remember that
adding a `sleep' to work around timestamp issues, with a minimum
granularity of one second, doesn't scale well for parallel builds
on modern machines with sub-second process completion.
`sort'
Remember that sort order is influenced by the current locale.
Inside `configure', the C locale is in effect, but in Makefile
snippets, you may need to specify `LC_ALL=C sort'.
`tar'
There are multiple file formats for `tar'; if you use Automake,
the macro `AM_INIT_AUTOMAKE' has some options controlling which
level of portability to use.
`touch'
If you specify the desired timestamp (e.g., with the `-r' option),
older `touch' implementations use the `utime' or `utimes' system
call, which can result in the same kind of timestamp truncation
problems that `cp -p' has.
On ancient BSD systems, `touch' or any command that results in an
empty file does not update the timestamps, so use a command like
`echo' as a workaround. Also, GNU `touch' 3.16r (and presumably
all before that) fails to work on SunOS 4.1.3 when the empty file
is on an NFS-mounted 4.2 volume. However, these problems are no
longer of practical concern.
`tr'
Not all versions of `tr' handle all backslash character escapes.
For example, Solaris 10 `/usr/ucb/tr' falls over, even though
Solaris contains more modern `tr' in other locations. Using octal
escapes is more portable for carriage returns, since `\015' is the
same for both ASCII and EBCDIC, and since use of literal carriage
returns in scripts causes a number of other problems. But for
other characters, like newline, using octal escapes ties the
operation to ASCII, so it is better to use literal characters.
$ { echo moon; echo light; } | /usr/ucb/tr -d '\n' ; echo
moo
light
$ { echo moon; echo light; } | /usr/bin/tr -d '\n' ; echo
moonlight
$ { echo moon; echo light; } | /usr/ucb/tr -d '\012' ; echo
moonlight
$ nl='
'; { echo moon; echo light; } | /usr/ucb/tr -d "$nl" ; echo
moonlight
Not all versions of `tr' recognize direct ranges of characters: at
least Solaris `/usr/bin/tr' still fails to do so. But you can use
`/usr/xpg4/bin/tr' instead, or add brackets (which in Posix
transliterate to themselves).
$ echo "Hazy Fantazy" | LC_ALL=C /usr/bin/tr a-z A-Z
HAZy FAntAZy
$ echo "Hazy Fantazy" | LC_ALL=C /usr/bin/tr '[a-z]' '[A-Z]'
HAZY FANTAZY
$ echo "Hazy Fantazy" | LC_ALL=C /usr/xpg4/bin/tr a-z A-Z
HAZY FANTAZY
When providing two arguments, be sure the second string is at
least as long as the first.
$ echo abc | /usr/xpg4/bin/tr bc d
adc
$ echo abc | coreutils/tr bc d
add
Posix requires `tr' to operate on binary files. But at least
Solaris `/usr/ucb/tr' and `/usr/bin/tr' silently discard `NUL' in
the input prior to doing any translation. When using `tr' to
process a binary file that may contain `NUL' bytes, it is
necessary to use `/usr/xpg4/bin/tr' instead, or `/usr/xpg6/bin/tr'
if that is available.
$ printf 'a\0b' | /usr/ucb/tr x x | od -An -tx1
61 62
$ printf 'a\0b' | /usr/bin/tr x x | od -An -tx1
61 62
$ printf 'a\0b' | /usr/xpg4/bin/tr x x | od -An -tx1
61 00 62
Solaris `/usr/ucb/tr' additionally fails to handle `\0' as the
octal escape for `NUL'.
$ printf 'abc' | /usr/ucb/tr 'bc' '\0d' | od -An -tx1
61 62 63
$ printf 'abc' | /usr/bin/tr 'bc' '\0d' | od -An -tx1
61 00 64
$ printf 'abc' | /usr/xpg4/bin/tr 'bc' '\0d' | od -An -tx1
61 00 64
File: autoconf.info, Node: Portable Make, Next: Portable C and C++, Prev: Portable Shell, Up: Top
12 Portable Make Programming
****************************
Writing portable makefiles is an art. Since a makefile's commands are
executed by the shell, you must consider the shell portability issues
already mentioned. However, other issues are specific to `make' itself.
* Menu:
* $< in Ordinary Make Rules:: $< in ordinary rules
* Failure in Make Rules:: Failing portably in rules
* Special Chars in Names:: Special Characters in Macro Names
* Backslash-Newline-Empty:: Empty lines after backslash-newline
* Backslash-Newline Comments:: Spanning comments across line boundaries
* Long Lines in Makefiles:: Line length limitations
* Macros and Submakes:: `make macro=value' and submakes
* The Make Macro MAKEFLAGS:: `$(MAKEFLAGS)' portability issues
* The Make Macro SHELL:: `$(SHELL)' portability issues
* Parallel Make:: Parallel `make' quirks
* Comments in Make Rules:: Other problems with Make comments
* Newlines in Make Rules:: Using literal newlines in rules
* Comments in Make Macros:: Other problems with Make comments in macros
* Trailing whitespace in Make Macros:: Macro substitution problems
* Command-line Macros and whitespace:: Whitespace trimming of values
* obj/ and Make:: Don't name a subdirectory `obj'
* make -k Status:: Exit status of `make -k'
* VPATH and Make:: `VPATH' woes
* Single Suffix Rules:: Single suffix rules and separated dependencies
* Timestamps and Make:: Subsecond timestamp resolution
File: autoconf.info, Node: $< in Ordinary Make Rules, Next: Failure in Make Rules, Up: Portable Make
12.1 `$
File: autoconf.info, Node: Failure in Make Rules, Next: Special Chars in Names, Prev: $< in Ordinary Make Rules, Up: Portable Make
12.2 Failure in Make Rules
==========================
Posix 2008 requires that `make' must invoke each command with the
equivalent of a `sh -e -c' subshell, which causes the subshell to exit
immediately if a subsidiary simple-command fails, although not all
`make' implementations have historically followed this rule. For
example, the command `touch T; rm -f U' may attempt to remove `U' even
if the `touch' fails, although this is not permitted with Posix make.
One way to work around failures in simple commands is to reword them so
that they always succeed, e.g., `touch T || :; rm -f U'. However, even
this approach can run into common bugs in BSD implementations of the
`-e' option of `sh' and `set' (*note Limitations of Shell Builtins:
set.), so if you are worried about porting to buggy BSD shells it may
be simpler to migrate complicated `make' actions into separate scripts.
File: autoconf.info, Node: Special Chars in Names, Next: Backslash-Newline-Empty, Prev: Failure in Make Rules, Up: Portable Make
12.3 Special Characters in Make Macro Names
===========================================
Posix limits macro names to nonempty strings containing only ASCII
letters and digits, `.', and `_'. Many `make' implementations allow a
wider variety of characters, but portable makefiles should avoid them.
It is portable to start a name with a special character, e.g.,
`$(.FOO)'.
Some ancient `make' implementations don't support leading
underscores in macro names. An example is NEWS-OS 4.2R.
$ cat Makefile
_am_include = #
_am_quote =
all:; @echo this is test
$ make
Make: Must be a separator on rules line 2. Stop.
$ cat Makefile2
am_include = #
am_quote =
all:; @echo this is test
$ make -f Makefile2
this is test
However, this problem is no longer of practical concern.
File: autoconf.info, Node: Backslash-Newline-Empty, Next: Backslash-Newline Comments, Prev: Special Chars in Names, Up: Portable Make
12.4 Backslash-Newline Before Empty Lines
=========================================
A bug in Bash 2.03 can cause problems if a Make rule contains a
backslash-newline followed by line that expands to nothing. For
example, on Solaris 8:
SHELL = /bin/bash
EMPTY =
foo:
touch foo \
$(EMPTY)
executes
/bin/bash -c 'touch foo \
'
which fails with a syntax error, due to the Bash bug. To avoid this
problem, avoid nullable macros in the last line of a multiline command.
On some versions of HP-UX, `make' reads multiple newlines following
a backslash, continuing to the next non-empty line. For example,
FOO = one \
BAR = two
test:
: FOO is "$(FOO)"
: BAR is "$(BAR)"
shows `FOO' equal to `one BAR = two'. Other implementations sensibly
let a backslash continue only to the immediately following line.
File: autoconf.info, Node: Backslash-Newline Comments, Next: Long Lines in Makefiles, Prev: Backslash-Newline-Empty, Up: Portable Make
12.5 Backslash-Newline in Make Comments
=======================================
According to Posix, Make comments start with `#' and continue until an
unescaped newline is reached.
$ cat Makefile
# A = foo \
bar \
baz
all:
@echo ok
$ make # GNU make
ok
However this is not always the case. Some implementations discard
everything from `#' through the end of the line, ignoring any trailing
backslash.
$ pmake # BSD make
"Makefile", line 3: Need an operator
Fatal errors encountered -- cannot continue
Therefore, if you want to comment out a multi-line definition, prefix
each line with `#', not only the first.
# A = foo \
# bar \
# baz
File: autoconf.info, Node: Long Lines in Makefiles, Next: Macros and Submakes, Prev: Backslash-Newline Comments, Up: Portable Make
12.6 Long Lines in Makefiles
============================
Tru64 5.1's `make' has been reported to crash when given a makefile
with lines longer than around 20 kB. Earlier versions are reported to
exit with `Line too long' diagnostics.
File: autoconf.info, Node: Macros and Submakes, Next: The Make Macro MAKEFLAGS, Prev: Long Lines in Makefiles, Up: Portable Make
12.7 `make macro=value' and Submakes
====================================
A command-line variable definition such as `foo=bar' overrides any
definition of `foo' in a makefile. Some `make' implementations (such
as GNU `make') propagate this override to subsidiary invocations of
`make'. Some other implementations do not pass the substitution along
to submakes.
$ cat Makefile
foo = foo
one:
@echo $(foo)
$(MAKE) two
two:
@echo $(foo)
$ make foo=bar # GNU make 3.79.1
bar
make two
make[1]: Entering directory `/home/adl'
bar
make[1]: Leaving directory `/home/adl'
$ pmake foo=bar # BSD make
bar
pmake two
foo
You have a few possibilities if you do want the `foo=bar' override
to propagate to submakes. One is to use the `-e' option, which causes
all environment variables to have precedence over the makefile macro
definitions, and declare foo as an environment variable:
$ env foo=bar make -e
The `-e' option is propagated to submakes automatically, and since
the environment is inherited between `make' invocations, the `foo'
macro is overridden in submakes as expected.
This syntax (`foo=bar make -e') is portable only when used outside
of a makefile, for instance from a script or from the command line.
When run inside a `make' rule, GNU `make' 3.80 and prior versions
forget to propagate the `-e' option to submakes.
Moreover, using `-e' could have unexpected side effects if your
environment contains some other macros usually defined by the makefile.
(See also the note about `make -e' and `SHELL' below.)
If you can foresee all macros that a user might want to override,
then you can propagate them to submakes manually, from your makefile:
foo = foo
one:
@echo $(foo)
$(MAKE) foo=$(foo) two
two:
@echo $(foo)
Another way to propagate a variable to submakes in a portable way is
to expand an extra variable in every invocation of `$(MAKE)' within
your makefile:
foo = foo
one:
@echo $(foo)
$(MAKE) $(SUBMAKEFLAGS) two
two:
@echo $(foo)
Users must be aware that this technique is in use to take advantage
of it, e.g. with `make foo=bar SUBMAKEFLAGS='foo=bar'', but it allows
any macro to be overridden. Makefiles generated by `automake' use this
technique, expanding `$(AM_MAKEFLAGS)' on the command lines of submakes
(*note Automake: (automake)Subdirectories.).
File: autoconf.info, Node: The Make Macro MAKEFLAGS, Next: The Make Macro SHELL, Prev: Macros and Submakes, Up: Portable Make
12.8 The Make Macro MAKEFLAGS
=============================
Posix requires `make' to use `MAKEFLAGS' to affect the current and
recursive invocations of make, but allows implementations several
formats for the variable. It is tricky to parse `$MAKEFLAGS' to
determine whether `-s' for silent execution or `-k' for continued
execution are in effect. For example, you cannot assume that the first
space-separated word in `$MAKEFLAGS' contains single-letter options,
since in the Cygwin version of GNU `make' it is either `--unix' or
`--win32' with the second word containing single-letter options.
$ cat Makefile
all:
@echo MAKEFLAGS = $(MAKEFLAGS)
$ make
MAKEFLAGS = --unix
$ make -k
MAKEFLAGS = --unix -k
File: autoconf.info, Node: The Make Macro SHELL, Next: Parallel Make, Prev: The Make Macro MAKEFLAGS, Up: Portable Make
12.9 The Make Macro `SHELL'
===========================
Posix-compliant `make' internally uses the `$(SHELL)' macro to spawn
shell processes and execute Make rules. This is a builtin macro
supplied by `make', but it can be modified by a makefile or by a
command-line argument.
Not all `make' implementations define this `SHELL' macro. Tru64
`make' is an example; this implementation always uses `/bin/sh'. So
it's a good idea to always define `SHELL' in your makefiles. If you
use Autoconf, do
SHELL = @SHELL@
If you use Automake, this is done for you.
Do not force `SHELL = /bin/sh' because that is not correct
everywhere. Remember, `/bin/sh' is not Posix compliant on many
systems, such as FreeBSD 4, NetBSD 3, AIX 3, Solaris 10, or Tru64.
Additionally, DJGPP lacks `/bin/sh', and when its GNU `make' port sees
such a setting it enters a special emulation mode where features like
pipes and redirections are emulated on top of DOS's `command.com'.
Unfortunately this emulation is incomplete; for instance it does not
handle command substitutions. Using `@SHELL@' means that your makefile
will benefit from the same improved shell, such as `bash' or `ksh',
that was discovered during `configure', so that you aren't fighting two
different sets of shell bugs between the two contexts.
Posix-compliant `make' should never acquire the value of $(SHELL)
from the environment, even when `make -e' is used (otherwise, think
about what would happen to your rules if `SHELL=/bin/tcsh').
However not all `make' implementations have this exception. For
instance it's not surprising that Tru64 `make' doesn't protect `SHELL',
since it doesn't use it.
$ cat Makefile
SHELL = /bin/sh
FOO = foo
all:
@echo $(SHELL)
@echo $(FOO)
$ env SHELL=/bin/tcsh FOO=bar make -e # Tru64 Make
/bin/tcsh
bar
$ env SHELL=/bin/tcsh FOO=bar gmake -e # GNU make
/bin/sh
bar
Conversely, `make' is not supposed to export any changes to the
macro `SHELL' to child processes. Again, many implementations break
this rule:
$ cat Makefile
all:
@echo $(SHELL)
@printenv SHELL
$ env SHELL=sh make -e SHELL=/bin/ksh # BSD Make, GNU make 3.80
/bin/ksh
/bin/ksh
$ env SHELL=sh gmake -e SHELL=/bin/ksh # GNU make 3.81
/bin/ksh
sh
File: autoconf.info, Node: Parallel Make, Next: Comments in Make Rules, Prev: The Make Macro SHELL, Up: Portable Make
12.10 Parallel Make
===================
Support for parallel execution in `make' implementation varies.
Generally, using GNU make is your best bet.
When NetBSD or FreeBSD `make' are run in parallel mode, they will
reuse the same shell for multiple commands within one recipe. This can
have various unexpected consequences. For example, changes of
directories or variables persist between recipes, so that:
all:
@var=value; cd /; pwd; echo $$var; echo $$$$
@pwd; echo $$var; echo $$$$
may output the following with `make -j1', at least on NetBSD up to 5.1
and FreeBSD up to 8.2:
/
value
32235
/
value
32235
while without `-j1', or with `-B', the output looks less surprising:
/
value
32238
/tmp
32239
Another consequence is that, if one command in a recipe uses `exit 0'
to indicate a successful exit, the shell will be gone and the remaining
commands of this recipe will not be executed.
The BSD `make' implementations, when run in parallel mode, will also
pass the `Makefile' recipes to the shell through its standard input,
thus making it unusable from the recipes:
$ cat Makefile
read:
@read line; echo LINE: $$line
$ echo foo | make read
LINE: foo
$ echo foo | make -j1 read # NetBSD 5.1 and FreeBSD 8.2
LINE:
Moreover, when FreeBSD `make' (up at least to 8.2) is run in parallel
mode, it implements the `@' and `-' "recipe modifiers" by dynamically
modifying the active shell flags. This behavior has the effects of
potentially clobbering the exit status of recipes silenced with the `@'
modifier if they also unset the `errexit' shell flag, and of mangling
the output in unexpected ways:
$ cat Makefile
a:
@echo $$-; set +e; false
b:
-echo $$-; false; echo set -
$ make a; echo status: $?
ehBc
*** Error code 1
status: 1
$ make -j1 a; echo status: $?
ehB
status: 0
$ make b
echo $-; echo set -
hBc
set -
$ make -j1 b
echo $-; echo hvB
You can avoid all these issues by using the `-B' option to enable
compatibility semantics. However, that will effectively also disable
all parallelism as that will cause prerequisites to be updated in the
order they are listed in a rule.
Some make implementations (among them, FreeBSD `make', NetBSD
`make', and Solaris `dmake'), when invoked with a `-jN' option, connect
the standard output and standard error of all their child processes to
pipes or temporary regular files. This can lead to subtly different
semantics in the behavior of the spawned processes. For example, even
if the `make' standard output is connected to a tty, the recipe command
will not be:
$ cat Makefile
all:
@test -t 1 && echo "Is a tty" || echo "Is not a tty"
$ make -j 2 # FreeBSD 8.2 make
Is not a tty
$ make -j 2 # NetBSD 5.1 make
--- all ---
Is not a tty
$ dmake -j 2 # Solaris 10 dmake
HOSTNAME --> 1 job
HOSTNAME --> Job output
Is not a tty
On the other hand:
$ make -j 2 # GNU make, Heirloom make
Is a tty
The above examples also show additional status output produced in
parallel mode for targets being updated by Solaris `dmake' and NetBSD
`make' (but _not_ by FreeBSD `make').
Furthermore, parallel runs of those `make' implementations will
route standard error from commands that they spawn into their own
standard output, and may remove leading whitespace from output lines.
File: autoconf.info, Node: Comments in Make Rules, Next: Newlines in Make Rules, Prev: Parallel Make, Up: Portable Make
12.11 Comments in Make Rules
============================
Never put comments in a rule.
Some `make' treat anything starting with a tab as a command for the
current rule, even if the tab is immediately followed by a `#'. The
`make' from Tru64 Unix V5.1 is one of them. The following makefile
runs `# foo' through the shell.
all:
# foo
As a workaround, you can use the `:' no-op command with a string
argument that gets ignored:
all:
: "foo"
Conversely, if you want to use the `#' character in some command,
you can only do so by expanding it inside a rule (*note Comments in
Make Macros::). So for example, if `COMMENT_CHAR' is substituted by
`config.status' as `#', then the following substitutes `@COMMENT_CHAR@'
in a generated header:
foo.h: foo.h.in
sed -e 's|@''COMMENT_CHAR''@|@COMMENT_CHAR@|g' \
$(srcdir)/foo.h.in > $@
The funny shell quoting avoids a substitution at `config.status' run
time of the left-hand side of the `sed' `s' command.
File: autoconf.info, Node: Newlines in Make Rules, Next: Comments in Make Macros, Prev: Comments in Make Rules, Up: Portable Make
12.12 Newlines in Make Rules
============================
In shell scripts, newlines can be used inside string literals. But in
the shell statements of `Makefile' rules, this is not possible: A
newline not preceded by a backslash is a separator between shell
statements. Whereas a newline that is preceded by a backslash becomes
part of the shell statement according to POSIX, but gets replaced,
together with the backslash that precedes it, by a space in GNU `make'
3.80 and older. So, how can a newline be used in a string literal?
The trick is to set up a shell variable that contains a newline:
nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"
For example, in order to create a multiline `sed' expression that
inserts a blank line after every line of a file, this code can be used:
nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"; \
sed -e "s/\$$/\\$${nl}/" < input > output
File: autoconf.info, Node: Comments in Make Macros, Next: Trailing whitespace in Make Macros, Prev: Newlines in Make Rules, Up: Portable Make
12.13 Comments in Make Macros
=============================
Avoid putting comments in macro values as far as possible. Posix
specifies that the text starting from the `#' sign until the end of the
line is to be ignored, which has the unfortunate effect of disallowing
them even within quotes. Thus, the following might lead to a syntax
error at compile time:
CPPFLAGS = "-DCOMMENT_CHAR='#'"
as `CPPFLAGS' may be expanded to `"-DCOMMENT_CHAR=''.
Most `make' implementations disregard this and treat single and
double quotes specially here. Also, GNU `make' lets you put `#' into a
macro value by escaping it with a backslash, i.e., `\#'. However,
neither of these usages are portable. *Note Comments in Make Rules::,
for a portable alternative.
Even without quoting involved, comments can have surprising effects,
because the whitespace before them is part of the variable value:
foo = bar # trailing comment
print: ; @echo "$(foo)."
prints `bar .', which is usually not intended, and can expose `make'
bugs as described below.
File: autoconf.info, Node: Trailing whitespace in Make Macros, Next: Command-line Macros and whitespace, Prev: Comments in Make Macros, Up: Portable Make
12.14 Trailing whitespace in Make Macros
========================================
GNU `make' 3.80 mistreats trailing whitespace in macro substitutions
and appends another spurious suffix:
empty =
foo = bar $(empty)
print: ; @echo $(foo:=.test)
prints `bar.test .test'.
BSD and Solaris `make' implementations do not honor trailing
whitespace in macro definitions as Posix requires:
foo = bar # Note the space after "bar".
print: ; @echo $(foo)t
prints `bart' instead of `bar t'. To work around this, you can use a
helper macro as in the previous example.
File: autoconf.info, Node: Command-line Macros and whitespace, Next: obj/ and Make, Prev: Trailing whitespace in Make Macros, Up: Portable Make
12.15 Command-line Macros and whitespace
========================================
Some `make' implementations may strip trailing whitespace off of macros
set on the command line in addition to leading whitespace. Further,
some may strip leading whitespace off of macros set from environment
variables:
$ echo 'print: ; @echo "x$(foo)x$(bar)x"' |
foo=' f f ' make -f - bar=' b b '
x f f xb b x # AIX, BSD, GNU make
xf f xb b x # HP-UX, IRIX, Tru64/OSF make
x f f xb bx # Solaris make
File: autoconf.info, Node: obj/ and Make, Next: make -k Status, Prev: Command-line Macros and whitespace, Up: Portable Make
12.16 The `obj/' Subdirectory and Make
======================================
Never name one of your subdirectories `obj/' if you don't like
surprises.
If an `obj/' directory exists, BSD `make' enters it before reading
the makefile. Hence the makefile in the current directory is not read.
$ cat Makefile
all:
echo Hello
$ cat obj/Makefile
all:
echo World
$ make # GNU make
echo Hello
Hello
$ pmake # BSD make
echo World
World
File: autoconf.info, Node: make -k Status, Next: VPATH and Make, Prev: obj/ and Make, Up: Portable Make
12.17 Exit Status of `make -k'
==============================
Do not rely on the exit status of `make -k'. Some implementations
reflect whether they encountered an error in their exit status; other
implementations always succeed.
$ cat Makefile
all:
false
$ make -k; echo exit status: $? # GNU make
false
make: *** [all] Error 1
exit status: 2
$ pmake -k; echo exit status: $? # BSD make
false
*** Error code 1 (continuing)
exit status: 0
File: autoconf.info, Node: VPATH and Make, Next: Single Suffix Rules, Prev: make -k Status, Up: Portable Make
12.18 `VPATH' and Make
======================
Posix does not specify the semantics of `VPATH'. Typically, `make'
supports `VPATH', but its implementation is not consistent.
Autoconf and Automake support makefiles whose usages of `VPATH' are
portable to recent-enough popular implementations of `make', but to
keep the resulting makefiles portable, a package's makefile prototypes
must take the following issues into account. These issues are
complicated and are often poorly understood, and installers who use
`VPATH' should expect to find many bugs in this area. If you use
`VPATH', the simplest way to avoid these portability bugs is to stick
with GNU `make', since it is the most commonly-used `make' among
Autoconf users.
Here are some known issues with some `VPATH' implementations.
* Menu:
* Variables listed in VPATH:: `VPATH' must be literal on ancient hosts
* VPATH and Double-colon:: Problems with `::' on ancient hosts
* $< in Explicit Rules:: `$
File: autoconf.info, Node: Variables listed in VPATH, Next: VPATH and Double-colon, Up: VPATH and Make
12.18.1 Variables listed in `VPATH'
-----------------------------------
Do not set `VPATH' to the value of another variable, for example `VPATH
= $(srcdir)', because some ancient versions of `make' do not do
variable substitutions on the value of `VPATH'. For example, use this
srcdir = @srcdir@
VPATH = @srcdir@
rather than `VPATH = $(srcdir)'. Note that with GNU Automake, there is
no need to set this yourself.
File: autoconf.info, Node: VPATH and Double-colon, Next: $< in Explicit Rules, Prev: Variables listed in VPATH, Up: VPATH and Make
12.18.2 `VPATH' and Double-colon Rules
--------------------------------------
With ancient versions of Sun `make', any assignment to `VPATH' causes
`make' to execute only the first set of double-colon rules. However,
this problem is no longer of practical concern.
File: autoconf.info, Node: $< in Explicit Rules, Next: Automatic Rule Rewriting, Prev: VPATH and Double-colon, Up: VPATH and Make
12.18.3 `$
File: autoconf.info, Node: Automatic Rule Rewriting, Next: Tru64 Directory Magic, Prev: $< in Explicit Rules, Up: VPATH and Make
12.18.4 Automatic Rule Rewriting
--------------------------------
Some `make' implementations, such as Solaris and Tru64, search for
prerequisites in `VPATH' and then rewrite each occurrence as a plain
word in the rule. For instance:
# This isn't portable to GNU make.
VPATH = ../pkg/src
f.c: if.c
cp if.c f.c
executes `cp ../pkg/src/if.c f.c' if `if.c' is found in `../pkg/src'.
However, this rule leads to real problems in practice. For example,
if the source directory contains an ordinary file named `test' that is
used in a dependency, Solaris `make' rewrites commands like `if test -r
foo; ...' to `if ../pkg/src/test -r foo; ...', which is typically
undesirable. In fact, `make' is completely unaware of shell syntax
used in the rules, so the VPATH rewrite can potentially apply to _any_
whitespace-separated word in a rule, including shell variables,
functions, and keywords.
$ mkdir build
$ cd build
$ cat > Makefile <$@
g.c: if.c g1.c
cat `test -f 'if.c' || echo $(VPATH)/`if.c g1.c >$@
h.c: if.c h1.c
cat `test -f "if.c" || echo $(VPATH)/`if.c h1.c >$@
Things get worse when your prerequisites are in a macro.
VPATH = ../pkg/src
HEADERS = f.h g.h h.h
install-HEADERS: $(HEADERS)
for i in $(HEADERS); do \
$(INSTALL) -m 644 \
`test -f $$i || echo $(VPATH)/`$$i \
$(DESTDIR)$(includedir)/$$i; \
done
The above `install-HEADERS' rule is not Solaris-proof because `for i
in $(HEADERS);' is expanded to `for i in f.h g.h h.h;' where `f.h' and
`g.h' are plain words and are hence subject to `VPATH' adjustments.
If the three files are in `../pkg/src', the rule is run as:
for i in ../pkg/src/f.h ../pkg/src/g.h h.h; do \
install -m 644 \
`test -f $i || echo ../pkg/src/`$i \
/usr/local/include/$i; \
done
where the two first `install' calls fail. For instance, consider
the `f.h' installation:
install -m 644 \
`test -f ../pkg/src/f.h || \
echo ../pkg/src/ \
`../pkg/src/f.h \
/usr/local/include/../pkg/src/f.h;
It reduces to:
install -m 644 \
../pkg/src/f.h \
/usr/local/include/../pkg/src/f.h;
Note that the manual `VPATH' search did not cause any problems here;
however this command installs `f.h' in an incorrect directory.
Trying to quote `$(HEADERS)' in some way, as we did for `foo.c' a
few makefiles ago, does not help:
install-HEADERS: $(HEADERS)
headers='$(HEADERS)'; \
for i in $$headers; do \
$(INSTALL) -m 644 \
`test -f $$i || echo $(VPATH)/`$$i \
$(DESTDIR)$(includedir)/$$i; \
done
Now, `headers='$(HEADERS)'' macro-expands to:
headers='f.h g.h h.h'
but `g.h' is still a plain word. (As an aside, the idiom
`headers='$(HEADERS)'; for i in $$headers;' is a good idea if
`$(HEADERS)' can be empty, because some shells diagnose a syntax error
on `for i in;'.)
One workaround is to strip this unwanted `../pkg/src/' prefix
manually:
VPATH = ../pkg/src
HEADERS = f.h g.h h.h
install-HEADERS: $(HEADERS)
headers='$(HEADERS)'; \
for i in $$headers; do \
i=`expr "$$i" : '$(VPATH)/\(.*\)'`;
$(INSTALL) -m 644 \
`test -f $$i || echo $(VPATH)/`$$i \
$(DESTDIR)$(includedir)/$$i; \
done
Automake does something similar. However the above hack works only
if the files listed in `HEADERS' are in the current directory or a
subdirectory; they should not be in an enclosing directory. If we had
`HEADERS = ../f.h', the above fragment would fail in a VPATH build with
Tru64 `make'. The reason is that not only does Tru64 `make' rewrite
dependencies, but it also simplifies them. Hence `../f.h' becomes
`../pkg/f.h' instead of `../pkg/src/../f.h'. This obviously defeats
any attempt to strip a leading `../pkg/src/' component.
The following example makes the behavior of Tru64 `make' more
apparent.
$ cat Makefile
VPATH = sub
all: ../foo
echo ../foo
$ ls
Makefile foo
$ make
echo foo
foo
Dependency `../foo' was found in `sub/../foo', but Tru64 `make'
simplified it as `foo'. (Note that the `sub/' directory does not even
exist, this just means that the simplification occurred before the file
was checked for.)
For the record here is how SunOS 4 `make' behaves on this example.
$ make
make: Fatal error: Don't know how to make target `../foo'
$ mkdir sub
$ make
echo sub/../foo
sub/../foo
File: autoconf.info, Node: Tru64 Directory Magic, Next: Make Target Lookup, Prev: Automatic Rule Rewriting, Up: VPATH and Make
12.18.5 Tru64 `make' Creates Prerequisite Directories Magically
---------------------------------------------------------------
When a prerequisite is a subdirectory of `VPATH', Tru64 `make' creates
it in the current directory.
$ mkdir -p foo/bar build
$ cd build
$ cat >Makefile <